Insects, other animals, and people

The bad news: Invaders from afar—general

The title of one of the reference articles for this chapter is “Humans as the world’s

greatest evolutionary force.”(367) While the article refers to the way humans have caused

disease bacteria and pests to develop resistance, it could equally be applied to the

penchant of humans to bring along friends and pests on trips. Even thousands of years

ago, humans brought invading species with them.(268,368) Hundreds of years ago,

Polynesian colonists brought pigs and rats to the islands of Polynesia. The Hawaiian

Islands went from receiving one new species every 50,000 years to one every 25 to 30

years after Polynesian colonization.(368) Now Hawaii receives about 20 new species each

year.(368) Humanity has caused an invasion of unprecedented proportions to take place,

leading to a mixing of what once had been geographically separate floras and faunas.(65)

We could classify this as a case of biological pollution.

Further, many invaders prosper in disturbed environments, such as those human beings

create when they go someplace new. Many species use “tricks” honed on their native

ground, as for example, the Centaurea diffusa plants that use root exudates to take over

foreign territory.(369)

America seems almost helpless against alien invaders. There may be many reasons for this

perception. For example, living in America, we might be more aware of successful

invaders from there to here than from here to there. However, there are several dimensions

to be considered. First, many invaders fail, and fail repeatedly. Second, the numbers of

successes is only about 2000 weedy plants (most of which came from Europe) and 2000

insects.(370)

Some species can become nightmares, and the cost of invaders is estimated at several

hundred million dollars annually for pesticides alone.(268,371) Many invasive species enter

a new home because of the global commercial shipping accompanying a truly global

economy. Seeds can be almost invisible, and be carried in packaging. However, most plant

introductions have been “on purpose,” at least according to some purpose of the one

person who imported them. Herbs have become more popular, and some have caused

problems in their new homes. Many places seem to cry out for ground cover to control

erosion, and history has shown that such plants especially can cause problems.(268) The

explosion of internet sites allows seeds to be bought with the click of a mouse, and the

mailed package containing the seeds is unlikely to be inspected. Such buyers are unlikely

to be aware of the Federal noxious weed list; the sellers are unlikely to care. With such

widespread commerce, there is virtually no followup on plant imports possible.

Insects can hitchhike on airplanes because of more and more direct flights between far-

flung locations. West Nile virus is thought to have entered the United States through a

mosquito that survived travel between an infected location and New York’s Kennedy

Airport. Many insects have evolved protective coloration, and by nature are small, hiding

inside packing materials such as straw and wood as they would in their natural home. In

addition, insects pass through quiescent stages, and lack of movement makes detection

difficult; after molting, the insect can become an invader. As has been pointed out by

many people, the use of sealed shipping containers to deter theft has made it particularly

easy for invaders to evade detection. Table E26.6.1 lists some invertebrate invaders.

TABLE E26.6.1

Selected Invertebrate Invasive Species

CommonName

ScientificName

Region ofOrigin

Region ofInvasion Comments Ref.

Argentine ant Linepithemahumile

SouthAmerica

California, Europe dynamic changes incommunityorganization

196,372

Asiancockroach

BlattellaasahinaiMizukubo

Asia entire world can spread disease a

Asian gypsymoth

Lymantriadispar

E. Siberia northeast &midwest U.S.

damage trees 130, a

cassavamealybug

Phenacococcusherreni

Africa damages cassava 130

citruslonghornedbeetle

Anoplophorachinensis

China Washington(possiblethroughout U.S.),northern China

destroy trees;destroyed 80million trees innorthern China

373

fire ant Solenopsisinvicta

SouthAmerica

southern UnitedStates

native ant speciesrichness is rapidlyreduced

196

giant Africansnail

Achatina(Lissachatina)fulica Bowdich

E. Africa Ohio, Wisconsin,Hawaii, NewZealand

carry disease threatto agriculture

374,375

grain borer Prostephanustruncates

S. America Africa spoils stored corn 130

gypsy moth Lymantriadispar

Europe, Asia eastern N. America feed on the foliageof hundreds ofspecies of plants

a

long hornedbeetle

Anoplophoraglabripennis(Motschulsky)

China Illinois, New York attack shade trees 130, a

Mediterraneanfruit fly

Ceratitiscapitata(Wiedemann)

subsaharanAfrica

subject toextermination twicein California. oncein Florida

fruit becomes juicyand inedible; lasteradication cost>$100M

a

olive fly Dacus oleae Mediterranean S. California larvae spoil olives aNew Zealandmud snails

Potamopyrgusantipodarum

New Zealand western U.S., LakeOntario

as dense as 750,000snails per m2, nativemollusks reduced

376

a Web searches conducted by author

The USDA Animal and Plant Health Inspection Service (APHIS) reports some 53,000

interceptions of arthropods, pathogens, and noxious plants arriving in the United States

per year.(377) APHIS inspectors cannot check everything, so this large number comes

from APHIS sampling of only about 2% of the materials! The National Academy

invasion study suggests many possible improvements that APHIS could make to help

decrease likelihood of invasions.(268) The fact that there is no worldwide database

covering introduced species is particularly striking. Larger animals seem less able to

invade successfully. Some of the few invasive vertebrate species are shown in Table

E26.6.2.

TABLE E26.6.2

Selected Vertebrate Invasive Animal Species

CommonName

ScientificName

Region ofOrigin

Region ofInvasion Comments Ref.

Africanclawed frog

Xenopuslaevis

Cooler regionsof sub-SaharanAfrica

parts of 11 states voracious eater,crowds out nativefish, amphibians

378

Monkparakeets

Mylopsittamonarchus

Caribbean southeast U.S. invaded 15 statesafter release fromcages

130

nutria Myocastorcoypus

southern SouthAmerica

Gulf coast,Chesapeake

destroy marsh,wetlands

379

python Pythonmolurus

Burma Everglades replaces nativesnakes

130

Many species that turn into nightmares are not invasive in their home ranges. And many

alien species that eventually turn into nightmares do not do so for many years after they

are introduced. In many cases, a five to ten year delay is typical.(255,380) In some cases, it

takes much longer for impacts to be judged. For example, Amur honeysuckle came to

North America in the late 1800s, and did not act as a weed until the 1950s.(249) While just

10% of species introduced are now considered problematic, the National Academy

invasion study warns that this could be because “the remaining 90% might be considered

innocuous only because their harmful effects have not been documented or even

investigated.”(268)

In Brandenburg, Germany, records show that of 184 species currently classed as invaders,

over half did not appear to be invasive for over two hundred years after their

introduction!(368) Christmasberry (Schinus terebinthifolius), valued by beekeepers in

Florida as a source of nectar during winter,(368) has invaded native ecosystems. While first

indications that the plant was in Florida can be traced back to the 1846, it was still not

noted in the wild as of 1941. By the mid-1950s, though, it was suddenly recognized as an

important invader.(368) Another example is the Brazilian pepper, which was present in

south Florida over a century ago. Only in the 1950s did the Brazilian pepper take on its

invasive character.(381)

It turns out that America does really welcome invaders more than Europe.(370) Ecologists

have suggested several reasons, but the most likely are ecological opportunity and

competitive superiority. The National Academy invasion study recommends scientific

study of “the structure and composition of natural ecosystems in North America (and the

disturbance regimes within them) . . . to analyze these ecosystems’ vulnerability to biotic

invasion. Attention should be paid to identifying groups of native species that could be

vulnerable or could facilitate the establishment of non-indigenous species.” The study also

recommends studying native American plants in their new homes to see which local

species can cause problems; these “problem species” could then be targeted for

interception.

As for opportunity, much more of America is forest than Europe, and much less

fragmented, giving a wider opportunity for species range. Some species that have gone

extinct in Europe still exist in America, opening niches in America that were closed down

in Europe. Because of the similarity in plants, America has many plants that European

insects can colonize, whereas some American specialists cannot colonize Europe because

the host is missing.(370) Ref. 370 deals with insects that eat plants, and asks whether

these could have any effect on success or failure of an invasion.

As to superiority, the authors of Ref. 370 note that the mean number of species of plant-

eating insects divided by the number of plant species is higher in Europe than in America.

This means that on average competition among the insects is more intense in Europe.

They also suggest that Europe might have been a site of intense competitive pressure that

honed native species into more efficient colonizers. There seem to be a greater number of

defenses among European genera than native American ones, indicating severe selection

pressures acted.

Also, timing matters, and European species would be find it easier to adjust to longer day

lengths at lower latitudes (on average) than American species to shorter day lengths at

higher latitudes (on average).(370)

There are various reasons for the superior performance of invaders. As of the early 2000s,

the best supposition is that invaders have left behind some of the parasites that rein them

in on their home territories (of course, they pick up new parasites in their new homes).

This is known as the “enemy release hypothesis.” Mitchell and Power in an experiment

examining plants report that “[o]n average, 84% fewer fungi and 24% fewer virus species

infect each plant species in its naturalized range than in its native range. In addition,

invasive plant species that are more completely released from pathogens are more widely

reported as harmful invaders of both agricultural and natural ecosystems.”(382) In another

experiment, this one on animals, Torchin et al. report that “[o]n average, 16 parasite

species were recorded from native populations of host species. Of these, an average of

only three parasite species successfully accompanied an invader to its introduced range.

In addition, an average of four new ‘native’ parasites colonized the introduced host. In

sum, introduced populations had roughly half the number of parasite species of native

populations.”(383) Taken together, these provide strong support for the enemy release

hypothesis.

The parasites that were brought along with the invasive species were as effective as in the

home territory. The less-prevalent parasites were the ones left behind.(383) Torchin et al.

claim that their work “is the first taxonomically broad quantitative support, using a

standardized analytical procedure, for the hypothesis that introduced species lose their

native parasites and that their colonization by new parasites does not make up for that

loss.”(383) Torchin et al. go on to say that their “results highlight the importance of

evaluating the role of parasites when examining the invasive species problem. ... the full

potential of biological control to mitigate invasive species has not been explored as

yet.”(383)

A commentary by Clay points out that the competing “ecological resistance hypothesis,”

in which native species and diseases keep invaders from spreading explosively, is unable

to “predict why certain species are more or less likely to invade that habitat,” while Refs.

382 and 383 can.(384) The studies lend “support to the idea that invasive species can be

controlled by speeding up their accumulation of parasites.”(384)

Some 50,000 species have invaded the United States as a result of human

intervention.(301) Invasions are the second-greatest cause of loss of biodiversity in the

United States after human disturbance.(255) Surprisingly, while invading species do well

where the ecosystem is disturbed,(255,385) some also appear to do well in undisturbed

very diverse ecosystems.(386) For example, in the Rockies, the more diverse test plots

were home to more invaders. This could be because rich biomes are able to support

exotics as part of their diversity.(386)

TABLE E26.6.3

Selected Invasive Fish Species

CommonName

ScientificName

Region ofOrigin

Region ofInvasion Comments Ref.

Asian carp Ctenopharyngodon idella

Asia MississippiRiver, ChicagoRiver

crowd out native fish,voracious

133

Asian swampeel

Monopterusalbus

E. & S. Asia FL, GA can travel overland,voracious eaters

387

bighead carp Hypophthalmichthysnobilis

China Midwesternrivers

reduce # of nativespecies

a

Eurasianround goby

Neogobiusmelano-stomus

Eurasia Great Lakes aggressive andvoracious feeders;eat native fish eggs;forage in totaldarkness

133, a

Eurasian ruffe Gymno-cephaluscernuus

Eurasia Great Lakes crowds out walleye,perch; outcompeteindigenous fish

133,387

European carp Cyprinuscarpio

Europe Australia takes overecosystems

130

grass carp Ctenopharyngoden idella

China U.S. introduced to controlweeds, destroysnative fish & fowlhabitat

a

largemouthbass

Micropterussalmoides

N. America Japan outperforms nativefish

a

Nile perch Latesniloticus

Nile River Lake Victoria half of species wentextinct

130

northern pike Esox lucius N. Alaska S. Alaska,California

invades Alaskanrivers, replacessalmon, outcompetesnatives

130,388

northernsnakehead

Channaargus

China MD, VA, FL,CA, AR

can live out of waterup to 4 days,voracious eater

387

rainbow trout Onchyno-chus mykiss

W. N. America many countries outeats native fish 130

round goby Neogobiusmelano-stomus

Black Sea,Caspian Sea

Great Lakes limit access to rockycrevices

387

sea lamprey Petromyzonmarinus

Atlantic coast Great Lakes(1800s)

eat indigenous fish,$15M/yr for control

133,365,387, a

a Web searches conducted by author

Invasive fish can be very successful outside their homes. One such “success story” is the

European invasion of the cyprinid fish, the Asian topmouth gudgeon (Pseudorasbora

parva).(a) The gudgeon was released in ponds alongside the Danube in Romania in the

1960s. It carries a parasite that devastates the native endangered European sunbleak

(Leucaspius delineatus), to which it is related.(a) The parasite can also attack other

species, such as the fathead minnow, and so poses “a threat to the conservation of

European fish diversity.”(a) Many other examples of the effects of invasive fish may be

found. Table E26.6.3 lists some invasive fish and Table E26.6.4 lists other aquatic

invasive species.

TABLE E26.6.4

Selected Aquatic Invasive Species

CommonName

ScientificName

Region ofOrigin

Region ofInvasion Comments Ref.

Chinesemitten crab

Eriocheirsinensis

China, Korea California burrow into riverbanks, outeat natives

376,389

Europeangreen crab,Europeanshore crab

Carcenusmaenas

Europe, N.Africa

Cape Cod,Chesapeake,Australia,S. Africa,N. America

eat shellfish(actually, everything),devastate ecosystems

387,a

quaggamussel

Dreissenaburgensis

Ukraine Great Lakes take over ecosystems 387

spiny waterflea

Bythotrephescederstroemi

Europe Great Lakes clog fishing gear a

veined rapawhelk

Raparavenosa

Sea of Japan Chesapeake change in ecology ofbottom-dwellers

387

zebra mussel Dreissenapolymorpha

Europe Great Lakes,many other lakes

control costs perhaps$30M/yr, clogseverything, damage>$60M/yr to powercompanies

130,133,390,391

a Web searches conducted by author

The estimated total yearly bill from exotic species that have invaded the United States is

about $140 billion.(251,371) Some 921 species native to America are under threat from

invaders.(251) That involves major cost in both senses.

The bad news: Invaders from afar—Yellowstone grizzlies at risk

A European import from the early part of the twentieth century, the European blister

rust fungus, could wipe out the whitebark pine in Yellowstone Park. If the climate is

warming as we think, the pine (which lives at high altitudes) will become more vulnerable

to European blister rust fungus.

Since whitebark pine is not a commercial tree, nothing is being done to stop the killer.

However, the Yellowstone grizzly bear depends on pine nuts hoarded by red squirrels to

fatten up in the fall, and Clark’s nutcracker depends on the nuts as well.(392)

The bad news: Invaders from afar—Dutch elm disease

Obviously, with the name Dutch elm disease, this is a foreigner (it was identified first in

the Netherlands around 1920, but was probably an invader from Asia).(393) It immigrated

into the United States in the late 1920s, and was found in Ohio in 1930.(394) As of 2001,

Dutch elm disease has destroyed about half of all American elm trees. The American elm,

Ulmus americana, is very vulnerable to the disease fungus Ceratocystis ulmi. The Siberian

elm is less vulnerable, but not resistant either.(394)

Both the American bark beetle and the European bark beetle spread the disease (see Fig.

E26.6.1). The Asian horned beetle (see the section “Invaders from afar—fire ants, the

longhorn beetle, and other insects,” below) is an additional danger. Lately, the disease

carried by these insects mutated and has become more virulent. There is still hope that

some elms will develop resistance or that horticulturists will be able to make a resistant

hybrid.(393)

Fig. E26.6.1 The elm bark beetle.(R. W. Stack, D. K. McBride, and H. A. Lamey, North Dakota State University Extension, Ref. 394)

As with the chestnut, for many years research focused on crosses with resistant Asian

varieties and back-crosses.(393) The resulting hybrids are not the same as the original

majestic American elms, and have not won wide acceptance.

More recently, genetic research using agrobacterium to transfer genes for resistance has

been attempted. Scottish scientists using the technique found they had produced a

resistant elm. It remains to be seen whether it is truly resistant.(393)

Invaders from afar—Formosan termites

Formosan termites (Coptotermes formosanus Shiraki) have invaded the southeast United

States, and is found from California to Virginia. Formosan termites are much more

destructive than native species.(395,396) In New Orleans alone, it is estimated that the

termites do $300 million of damage each year. So far, insecticide and trapping have been

the measures of choice, but this has had limited success with entrenched populations.(395)

The bad news: Invaders from afar—the emerald ash borer

The emerald ash borer (Agrilus planipennis) is currently destroying ash trees in Indiana,

Maryland, central and southern Michigan, and northwest Ohio (see Fig. E26.6.2).(397)

The only way to deal with the invasion is to cut the trees down and burn them because

the ash borer is lethal to ash (Fraxinus sp.). The ash trees die within two to three years of

infection but trees do not show any effects until shortly before they die.(397) Millions of

trees in Michigan and thousands of trees in the vicinity of Toledo, Ohio have been cut

down.(398,399) Over $14 million has been spent to fight the infestation. The ash borer

could travel a long way if it’s not stopped in Indiana and Michigan; Illinois and Wisconsin

have millions of ash trees to tempt the ash borer should it escape the cordon.(400)

Fig. E26.6.2 The emerald ash borer; infested regions shown in dark green (2002), light green (2003), andyellow (2004).(Forest Service, U.S. Department of Agriculture, “Emerald ash borer,” URLhttp://ncrs.fs.fed.us/4501/eab/maps/)

Apparently some people have taken cut ash home for firewood, carrying the ash borer to

new sites of infestation.(b,c) Insecticides alone are useful but not sufficient for the task of

stopping the invasion.(d) Thousands of ash trees in Indiana, Michigan, Ohio, and Ontario

have already been skinned as traps for the borer.(c) Skinned trees release a pheromone that

indicates distress and attracts the ash borers. A sticky substance called Tanglefoot is

applied to the trees, so that when the ash borers are attracted to the tree in distress the

insects are trapped.(c)

Ohio’s war against the ash borer is being waged in the Toledo area adjacent to the infested

regions of Michigan, where nearly 30 million trees have been affected or removed to

prevent infection.(c) About 10% of Ohio’s trees (about 3.8 billion) are ash, and the state

may lose as much as $3 billion over a decade if the ash borer is not controlled.(b,d) Toledo

Blade reporter Tom Henry writes:(d)

The ash borer has been called the biggest threat to a tree species since Dutch

elm disease wiped out the American elm decades ago. Dutch elm disease began

in Cleveland in 1930. By the 1960s, the elm - one of the nation’s most

popular shade trees - was virtually gone.

“Diversify, diversify, diversify,” said Robert Gentry, Adrian parks and

forestry superintendent. He said Americans apparently didn’t learn that

lesson from the elm and now will learn it again the hard way from the loss of

the ash. Ironically, ash trees replaced many elm trees as shade trees.

The threat is dire. According to another news report in the Toledo Blade, “Lest there be

any doubt that North America’s billions of ash trees are imperiled by the deadly emerald

ash borer, consider this:(e) The government is establishing a national gene pool to help

keep the shade trees from going extinct.” The seeds will be sent to the National Center for

Genetic Resources Preservation in Colorado.(e)

The bad news: Invaders from afar—snails and snakes

The introduction of a single pair of African snails into the Miami area in 1967 led to an

infestation within 3 years, one which cost $500,000 to eradicate.(401) The introduction of

the giant snail Achatina fulica into Hawaii in 1936 caused introduction of 16 other species

(7 beetles, 2 flies, 7 snails) in the attempt to control A. fulica.(117)

The golden apple snail (Pomacea canaliculata) was introduced into the Philippines from

Taiwan, where it had been imported from Argentina as a source of protein for people and

animals. It took over, and is a pest all over Asia because it exhibits a taste for rice.(402,368)

The golden apple snail cost Philippine farmers somewhere between $28 and $45 million

in just one year, about 40% of annual expenditures for imports of rice.(368)

The brown tree snake (Boiga irregularis) comes from Papua-New Guinea. It has stowed

away on planes and ships and now is present on most islands in the south Pacific.(403)

On Guam, the snake has wiped out nine of eleven of the native forest birds and four

species of lizards. It has raised great concern in Hawaii, as it keeps finding its way in

before being found and exterminated.

The bad news: Invaders from afar—the zebra mussel and other aquatic invaders

We don’t always choose the immigrants. The zebra mussel (Dreissena polymorpha) came

over in a ship’s bilge sometime in the 1980s.(251,404) In fact, it had been brought in to the

Great Lakes many times before, but had never gained a foothold. Ship ballast is the major

source of Great Lakes invaders (and invaders in other places with ports, such as San

Francisco and Mobile).(134,196,365,373,376,389,391,398,405) It would be possible to modify

the ships’ ballast handling systems. This modification would cost about $0.5 million per

ship; so it would cost about $200 million for the ~400 ships that commonly enter the

Great Lakes to be modified.(391,406)

Apparently the increasing quality of Great Lakes water made the zebra mussel invasion

possible.(255) The invasion by this one pest alone costs an estimated $100 million per

year in control measures (see Table E26.6.4).(251) The cumulative cost was expected to

reach $5 billion by 2002.(407) Thus, ballast modification seems like a good economic

choice for the governments involved.

I am focusing on the Great Lakes not only because I live in Ohio, a Great Lake state, but

also because the Great Lakes have been so open to invasion and because of the huge

geographic area represented by the Great Lakes (as compared to, for example, Chesapeake

Bay or the much more compact San Francisco Bay). In the nineteenth century, the Great

Lakes were invaded by 43 species; in the twentieth, by 127 species—and the pace has

been accelerating (Fig. E26.6.3).(133)

interval

Ave

rage

num

ber o

f spe

cies

inva

ding

the

Gre

at L

akes

per

yea

r

0

0.5

1

1.5

2

2.5

1810-39 1840-69 1870-99 1900-29 1930-59 1960-89 1990-now

Fig. E26.6.3 Average number of species per year invading the Great Lakes.(Adapted from information in Ref. 133)

As with ecosystems on land, disturbed marine ecosystems seem also to be more likely to

be invaded.(408) In a marine system made up of mussels and other native aquatic

invertebrate species, the most diverse plots showed the least amount of alien

invasion.(408)

It has been estimated that 99% of all biomass in San Francisco Bay in not native.(255) In

many places, over 90% of species are aliens.(f) Between 1851 and 1960, only about one

new species per year established itself in the Bay. Between 1960 and 1995, the rate was

one new species about every three months.(368,409) The total number of invaders in the

Bay exceeds 230, more than either the Great Lakes (~170) or Chesapeake Bay

(~200).(130,391) Thus, the rate on San Francisco Bay invasions is also accelerating.(196)

The Chesapeake Bay is so polluted that native oysters have been nearly wiped out by

two parasites. There have been proposals to stock the Bay with parasite-resistant Asian

Suminoe oysters (Crassostrea ariakensis), but a study by the National Academy of

Sciences suggested that among the three options considered—doing nothing, waiting and

doing further research, introducing the Suminoe oysters—waiting is the best choice.(410)

The Asian Suminoe oyster had already been introduced into New Zealand and Australia,

where it adversely affected the native species. The Academy proposed that a very small-

scale experiment with sterilized oysters be conducted over a five-year period before

making any decision to release fertile oysters.(410)

The bad news: Invaders from afar—fire ants, the longhorn beetle, and other insects

Perhaps the worst insect pest released in the United States is the fire ant, which made its

way into the country through Mobile, Alabama, in 1918. The stings of the ant can cause

blisters and (occasionally) allergic reactions. To try to control the ant, the federal

government supported application of the insecticide Mirex to the tune of $148 million.

The program was canceled because the insecticide has been implicated in fish kills and

may cause cancer (it is one of the “dirty dozen” chemicals).(411)

Ants continue to spread, especially in Mediterranean-type climates, but the invasion

problem has not received much attention.(412) Ants introduced by humans can easily

become invasive (as the fire ant has). They hold the promise of causing major changes in

the ecosystems they are brought to, as recent research in South Africa on the Argentine

ant has shown.(412) Interestingly, in 2004 a 100 km wide Argentine ant supercolony

marched on Melbourne, Australia.(413)

It cost $11 million to eradicate the Mediterranean fruit fly (medfly) from Florida in the

late 1960s.(414) It cost far more to eliminate the medfly from California in the 1981

infestation (around $100 million).(404,415) The medfly continued to appear occasionally in

California and Florida in the 1980s and 1990s, raising doubts as to the possibility of true

eradication.

Fig. E26.4.4 The Asian long horned beetle (Anoplophora glabripennis).(USDA)

The Asian longhorn beetle has been found in New York City and Chicago (Fig. E26.4.4).

It very probably arrived on wooden packing crates and pallets from China (Fig. E26.4.5)

around 1996.(416,417) In Chicago, in an attempt to scotch the invasion some 1,400 trees

were felled and others inoculated with insecticide imidacloprid, which worked well on the

beetle in tests conducted in China.(251,418,419) New York City adopted similar measures,

cutting down 5,000 trees between 1996 and 2001.(419) The Asian longhorn beetle

infestation in the town of Amityville on Long Island cost the town more than $1

million.(420) The estimated cost to the American economy if the beetle gets loose to

spread is $138 billion.(420)

Fig. E26.4.5 The Asian long horned beetle larvae in a shipping crate.(USDA)

The bad news: Australian mistake squared—European rabbits and red foxes

Domestic European rabbits (Oryctolagus cuniculus) were brought to Australia in 1859 to

shoot for sport. However, they escaped and eventually took over native Australian

ecosystems. The original twenty-four were soon millions, and Australians looked for

ways to control them. In 1868, the red fox (Vulpes vulpes) was imported to Australia. A

predator of the rabbit at home in England, it found easy pickings among native Australian

animals.(403) This illustrates the point that vertebrate animals are generally too

omnivorous and opportunistic to choose as a good biocontrol.

The Australians eventually found they could use a disease, myxomatosis (rabbit

hemorrhagic disease), which was caused by the myxoma virus, to help control (but not

extirpate) the rabbits. At its release in the 1950s, myxomatosis killed over 99% of rabbits,

but because of resistance buildup in rabbits and attenuation of the virus, mortality is

around 50% as of 2005. Today, the Commonwealth Scientific and Industrial Research

Organization (CSIRO) in Australia estimates the economic damage from European rabbits

at over $600 million per year. More recently, Australia and New Zealand has used

calicivirus to try to control the rabbits.

The bad news: The giant cane toad

The cane toad (Bufo marinus) was imported into Australia and many Caribbean and

Pacific islands to control several beetles that prey on sugar cane. Unfortunately, the toad

was an equal-opportunity eater and attacked native fauna instead of its intended target

(see Table E26.6.5). It is now a major pest in Queensland, Australia, and elsewhere in the

Pacific. Nothing the Australians have tried has been able to remove these toads from the

environment.(403)

The bad news: The “blob that ate the Black Sea”(421)

The American Atlantic coast jellyfish, Mnemiopsis leidyi, was brought in ballast water to

the Black Sea region about 50 years ago. M. leidyi is harmless in its native region, but is

one of the most noxious invaders ever encountered in the Black Sea.(422) M. leidyi found a

sort of jellyfish heaven in the Black Sea and “munched its way through the eggs and larvae

of a wide variety of fish, while consuming the plankton on which other fish fed.”(421) In

the late 1990s, it moved into the rich Caspian Sea, home of the sturgeon that produce

caviar.(421)

The bad news: Alien fish have arrived in America!—carp

It has been found that various foreign seaweed, fish, parasites, and disease organisms

follow the introduction of fish aquaculture.(363) Mollusk aquaculture has been practiced

for over a century with few ecological problems.(363) However, growing fish can cause

many problems. See the section “Problems of husbandry” in Extension 26.4, Interspecies

competition, habitat, and ecosystem services.

A case in point is the use of black carp to control trematodes of catfish.(363,423) Carp eat

mollusks indiscriminately, and freshwater mussels are among the most endangered species

in North America. Most farmers recognized the danger the carp posed and used sterile

carp for pest control, but the situation became dire in 1999, when a new trematode

outbreak threatened catfish farmers and many used “normal” carp, which might be able to

escape from the hatcheries.(363,423)

There is great concern that Asian carp (Hypopyhalmichthys nobilis) will reach the Great

Lakes because of the voraciousness of the fish. A fish farmer in Arkansas released them

into the wild in the 1980s and they have outcompeted many native species.(390) This carp

could destroy the remaining ecosystem of the Lakes.(365,405)

Because of the magnitude of the problem—and desperation—an electric barrier is being

built in the Chicago Sanitary and Ship Canal to prevent the carp from reaching Lake

Michigan.(398,424) The barrier works in tests, but it remains to be seen whether the

electric barrier will work when it is place—and despite not knowing the answer, a second

electric barrier is being built.

The carp are dangerous to native species in this new environment, and different species

have escaped into midwestern rivers. Silver carp have been known to flip nearly 3 m out

of the water and injure boaters.(133,425) Given the invasive nature of all carp, it may come

as a surprise that Texas as late as 2003 introduced the grass carp to control hydrilla.(426)

An earlier introduction in Lake Conroe, Texas, resulted in ruination of the lake.(426)

The bad news: Alien fish have arrived in America!—catfish

Flathead catfish (Pylodictis olivaris) are found in streams in the American midwest. It

came as a complete surprise when one was found in the Delaware and Raritan Canal in

New Jersey in July, 2004. The catfish has a reputation as a “voracious predator that has

decimated native populations of other catfish, certain species of sunfish and rare species

of sturgeon in the southeastern United States.”(427) One report on the invasion was titled

“The Insidious Flathead Catfish.”(428) It counsels

Flatheads, top predators in most river systems, are active hunters, feeding

primarily at night. They need to consume large quantities of fish to fuel their

rapid growth rate. This species is efficient at hunting prey at night because of

its specialized electroreceptor cells and enhanced olfactory sense. Studies of

flatheads in their native watersheds demonstrate low population densities,

fairly sedentary behavior, and restriction to fresh water. However, in recent

studies, fishery biologists have discovered that in rivers where they have been

introduced, the catfish are found in high densities, are highly mobile, and are

tolerant of salinities of up to 6 parts per thousand. These data suggest that

they are capable of feeding in the Delaware Bay estuary.

Since the catfish have been reported in the Delaware River in the late 1990s,(428) it is

going to be very hard to defeat this catfish invasion.

The bad news: Alien fish have arrived in America!—lionfish

Lionfish (Pterois volitans) are native to the Pacific Ocean, but during the month of

August, 2004, many were found in the Atlantic.(429) Lionfish were first seen in the

Atlantic in 2000, and no one knows how they arrived (they may have gotten out of

aquaria during Hurricane Andrew, or came in ballast water).(430) Lionfish eat reef fish and

do not seem to be eaten by other Atlantic fish.(429) They are about a kilogram full grown.

Naturalists are resigned to living with them. In addition to being voracious eaters, they can

sting humans (and it is reported to be very painful, though not life-threatening).(430) It

had been hoped that lionfish could not breed in the Atlantic, but that hope was—

obviously—dashed.(429)

The bad news: Alien fish have arrived in America!—the snakehead

The northern snakehead (Channa argus) arrived in America from China. In 2002, the first

discovery of the snakehead in a Maryland pond by a local angler unleashed a media circus.

Ken Ringle, of the Washington Post, wrote somewhat breathlessly:(431)

The walking fish in question (tentatively identified as Channa argus argus)

appear to be based in a pond behind a shopping center in Anne Arundel

County, where they presumably immigrated by unknown means from their

native China. It is not known how long they have been in Crofton, but so far

two have been caught, one 19 inches long and one 26 inches.

Since the snakehead fish is extremely aggressive, is indiscriminate in its eating

habits and reportedly grows to 40 inches and 15 pounds, one might surmise it

has yet to exhaust its food supply in greater Crofton. If it had, instead of

inhaling hooked minnows hung from the poles of 12-year-old bounty anglers,

it would be hiking hungrily down Route 3 to the next town, Bowie.

a.

b.

Fig. E26.6.6 a. Northern snakehead adult.[Ref. 433 (from Cantor, 1842), 45] b. The toothy maw of the snakehead.(Photo by Walter R. Courtenay, Jr. USGS, Ref. 433)

The assertion that the fish walks on land is something of an exaggeration (young snakefish

can wriggle across land from one body of water to another, but not adults of most

species). The snakefish can stay alive for up to four days out of water, however, and has

a set of extremely sharp teeth (Fig. E26.6.6). The presumed culprit was someone who

bought the fish for an aquarium and then later released them to avoid killing them. The

snakehead is a delicacy in China, so if it were to have been imported by Chinese or

Koreans living in the Washington region, it would have been eaten rather than released.

After the discovery, Maryland officials prodded the water with electric prods and

ascertained that several fish were still there. They ultimately decided to poison the

pond. (432) Fish importers were barred from importing the snakehead after August,

2002.(433) After the success of that poisoning, Maryland (and the press’s readers)

breathed a sigh of relief: the emergency was over.(434)

The relief did not last long. In the summer of 2004, more snakehead were found in a

Wheaton, Maryland, lake and in the Potomac River, the border between Maryland and

Virginia.(435) The Washington Post editorialized “Attack of the Killer Fish,”(436) which

began “They look like aliens from a science fiction movie,” (actually, the rest of the

editorial was a sensible discussion of invasive species). More of the fish were caught in

Maryland and Virginia. The circus was on again—the “frankenfish” was loose.(437)

The importation ban was apparently ineffective. In the summer of 2004, a grocer in Los

Angeles’s Koreatown was arrested for importing snakeheads. According to the article,

“[i]t’s illegal to import live snakeheads into the United States for sale. But federal

prosecutors said markets in heavily Korean communities find ways to sneak in the live

fish.”(438) The fish were apparently labeled as “sea bass” and imported from Korea

concealed among legal imports.

Are the snakefish dangerous? The answer is not yet known definitively. The U.S.

Geological Survey writes:(433)

During all life stages, snakeheads compete with native species for food and

habitat. As juveniles, they eat zooplankton, insect larvae, small crustaceans,

and the young of other fishes. As adults, they become voracious predators,

feeding on other fishes, crustaceans, frogs, small reptiles, and sometimes birds

and small mammals. Should snakeheads become established in North

American ecosystems, their predatory behavior could drastically disrupt food

webs and ecological conditions, thus forever changing native aquatic systems

by modifying the array of native species.

The U.S. Fish and Wildlife Service makes similar points.(439)

The three biggest reasons to be concerned about snakeheads are: 1) these fish

are very predatory and could alter the balance of our ecosystems, 2) these fish

are air-breathers and are capable of overland migration, 3) these fish are very

aggressive in their efforts to protect their young. When these factors are

combined, snakeheads pose a significant threat to native fish and wildlife

resources.

The Fish and Wildlife Service also points out the danger that pathogens such as Epizootic

Ulcerative Syndrome could be transferred to native fish.(439)

Concern is certainly warranted, of course, given the sorry history of past invasions, but

the snakehead may have already become a permanent addition to the Potomac ecosystem.

Hysteria is probably not warranted. Life may well go on as in the past, with the addition

of one predatory fish.

State officials are not yet giving up. Natural Resources Departments from both states

have been stunning fish in the Potomac with electricity to find out whether the dozen or

so catches are the harbinger of a real invasion (the multiplicity of landings indicates it is)

or just a few isolated individuals released from aquariums.(437,440) Fingerlings have been

found, which is not a good sign.(440) The Potomac couldn’t be drained or poisoned as the

Crofton pond was.

In addition, snakeheads have been discovered in 2004 in Massachusetts, Pennsylvania,

and Illinois. These are smaller in scale than the Maryland-Virginia invasion, and there is a

good chance that the snakehead can be extirpated from these other locations.(440)

The bad news: Invasive earthworms?

Yes, that’s right. In many parts of North America, the parts covered in glaciers during the

last ice age, the glaciers wiped out the earthworms. Pretty much east of the Rockies in

Canada and in the northern United States, any earthworms are invaders (at least in some

sense).(441) The earthworms are taking over ecological niches that did not have inhabitants

before they came, so some would characterize them as “introduced species,” a more

neutral term. However, they are in the process of destroying unique ecosystems, and that

seems a more apt way for us to categorize whether something is an “invader.” Many

earthworms are invaders by that criterion.

We heard as children about how good earthworms are for the soil. This is true for most

soils, because earthworms churn, aerate, and fertilize these soils. Earthworms can increase

availability of nutrients and water to plants. Worms are an essential part of composting.

In Canada and the upper Midwest are found soils known as “duff.” Duff is a spongelike

material that springs up and down as animals walk on it. Eastern Canada, Minnesota,

upper Michigan, North Dakota, and parts of South Dakota are home to such duff soils

and a unique earthwormless ecosystem. When earthworms do their plowing on duff soils,

the duff melts away, cycled into the dirt underlying the duff.(442) The local flora—plants,

especially beautiful wildflowers found nowhere else—go away with the duff, as do

animals such as salamanders. Buckthorn replaces oak.(442)

There are almost 100 native American species of earthworm (70 in the east and south, 28

along the Pacific). Native earthworms come from the families Komarekionidae (found

only in North America), Lumbricidae, and Megascolecidae.(441) About 50 non-native

species have arrived from the major continents.

European native earthworms such as Lumbricus terrestris (nightcrawlers) and

Luumbricus rubellus (redworms) have been coming into America since humans came in

ships from Europe, but they can only travel a few meters per year on their own. The

invading earthworms in the upper Midwest and Canada come as bait dumped by

fishermen, carried along inside tire treads of off-road vehicles, in root balls of trees and

ornamental plants, or are brought in loads of soil from elsewhere.(441,442)

Importation of earthworms is prohibited by APHIS, which is responsible for protecting

and promoting U.S. agricultural health, not so much over concern about invasion by the

worms themselves, but because they can carry bacterial and viral pathogens in their

guts.(441) Many earthworms come anyway in root balls of imported plants.

Not every act of earthworms is benign. Earthworms can remove soil cover that prevents

erosion. They can spread seeds of weeds in gardens. In some circumstances, they can

decrease soil nitrogen and carbon levels. They can riddle irrigation ditches, making them

useless. As mentioned above, they may also spread pathogens to both plants and animals

(they spread hoof and mouth disease in cattle, for example). Earthworms can carry

nematodes such as pinworm, intestinal parasites such as flukes, and protozoa that cause

diseases such as sleeping sickness that infect birds and domestic animals.(441)

Overall, whether the earthworms are beneficial or not will depend on particular

circumstances. In most cases, they are beneficial overall. But as invaders, they can

destroy unique ecosystems such as the duff. In areas already colonized by native

earthworms, invasions provoke less drama (at least as seen from the surface). It seems

that native species are best adapted to undisturbed soil and local climatic conditions, but

when disturbances occur (plowing, etc.), invaders can outcompete native species.(441)

The bad news: Wildlife at risk from chemical spills

Gold mining is risky environmentally, since the typical gold extraction process uses

cyanide. If cyanide spills, fish and wildlife can be endangered. In 1995, cyanide spilled

into the Essequibo River in Guyana. In 1998, the spill was into the Gradiamar River that

runs through Donana National Park in Spain. In 2000, it was a gold mine in Romania that

dumped cyanide, zinc, lead, and copper into the Tisza River into Hungary and the

Danube.(443) At least 200 tons of dead fish were found in the Tisza. Many other fish in

the Danube died as well. Two species of fish endemic to the Tisza may have become

extinct. Dead eagles were found in Hungary.

In view of the push to drill at the Arctic National Wildlife Refuge, it is instructive to look

at other refuges where the Fish and Wildlife Service has permitted drilling (look at

Extension 12.1, Politics and fossil fuels). A number of significant spills have occurred in

Louisiana, where these sites are found. Large areas of marsh were affected in some spills,

but no effects on wildlife documented.(444) Of course, conditions in Alaska are less

forgiving than in Louisiana.

The bad news: The Endangered Species Act

The Endangered Species Act remains controversial three decades after it passed. Lawsuits

mire the Fish and Wildlife Service in trying to answer, and prevent the agency from

investigating and listing new species.(445) Once a species has been listed, the Federal

Government is not allowed to approve any project that could harms that species. The

agency is being sued mostly because it has designated the critical habitat for just 133

species (about 1200 species are listed altogether),(445) and faces court orders to designate

300 species’ habitats.(87) The Fish and Wildlife Service declared a moratorium in 2001 to

attempt to deal with these pressures.(446) Everyone agrees that there must be a new focus

in a revised Endangered Species Act on compensating those who must provide the

protection to the species.(446) The cost of listing may be even more difficult to cope with.

It costs about $71,000 to list a species as endangered.(446)

Of course, listing species has consequences, money consequences. That is the reason for

the continuing controversy. To be able to log in the Northwest, for instance, according to

the 1994 Northwest Forest Plan, effects on some 340 species must be surveyed and

cataloged.(447)

We know that people have been responsible for the extinction of the mammoth, the dodo,

and also the moa. The original population of ancestors of the Maoris drove the eleven

species of moas that lived in New Zealand to extinction in less than a century.(448) There

are indications that we are causing unprecedented extinctions, and it is important to keep

as much of our patrimony as we can.(449)

The good news: Controlling overfishing

How should one use available statistics to protect fisheries? As with other precautionary

efforts, one should look at the possible effect in the worst case, and make a decision on

that basis (that is, if this goes on the worst that could happen is ...).(320) Prudence would

dictate, in the case of fishing, that take be limited. Unfortunately, fishermen have not yet

figured out what is happening to them—they are too close to be able to see where their

self-interest lies (again because it seems that the resource belongs to everyone). They

prefer to look at the problem, and say, but if there were no effect, then we could take

larger catches.(320) They ignore the possibility that the worst might happen. Of course,

sometimes there is no effect. Precaution would not have hurt if the prudent thing had been

chosen, except in the pocketbook of the fisherman. But when there is an effect, the lack of

preparation drives the situation worse very swiftly. (See also the discussion in Extension

26.5, The oceanic food web.)

The ocean is huge, and there is probably still time to save many endangered species. The

fisheries experts are united in their desire for a reserves (refugia, or refuges)

policy.(317,319,347,450,451) The refuges need to be places where there is no fishing. In the

past, fishermen could argue that it was not certain that setting reserves aside would help.

Research has come to assist scientists in communicating the evidence. No-fish zones are

predicted to benefit the localities they are near the zones the most, so it should be

possible to get local agreement.(347,450) And actual measurements off St. Lucia have

shown that reserves do actually aid fisheries.(451) Both commercial catches and trophy

fish catches increased. The reserves constitute the “real ocean,” while the ocean is another

of the human experiments on large scale (similar to the one inducing climate change).

The hope is that the reserves can save the whole oceanic web of life. President Clinton

presumably had this in mind when he created the Northwestern Hawaiian Islands Coral

Reef Reserve, an area off Hawaii’s coast that is as large as the states of Georgia and

Florida together, an area containing most of the coral reefs in America, and one with

restricted fishing to help keep fisheries alive.(452)

The good news: The value of quick action

The example of the invasion that wasn’t in Australia is instructive. Mussels similar to the

zebra mussel were found in Darwin, Australia in early 1999, where none had been just a

few months earlier. The Australian Northern Territory government quarantined the

marinas, and poisoned the marinas with $1.5 million worth of chlorine and copper, which

killed everything. The region has been free of further invasion and the ecosystem has

returned to normal.(417)

The good news: The value of commitment

The nutria (a rodent) was imported to Britain for its fur in the 1920s from South America.

Nutria soon escaped from farms. Despite an established population, some 200,000

strong, and poor success at removal of invaders who became established elsewhere,

attempts to eradicate them from their 12,500 km2 British range began. The first attempt,

which began in the 1960s was unsuccessful, but the British kept at it and did further

research on the habits of the rodent. The second attempt, which involved trapping the

animals, was launched in the early 1980s, and succeeded.(453) The persistence of the

British won this battle and shows that rollback is possible if the commitment is there and

is total.

The good news: Choosing invaders

Of course, humans bring with them exotics we don’t even think about, and don’t regret.

Wheat, corn, barley—all are foreign species brought to America by immigrants who

wanted familiar crops.

In the last few centuries, ecologists have released over 300 sorts of insects, spiders, and

diseases in attempts to eliminate (or at least control) 50 unwanted plants. They have also

released nearly 1000 biocontrol attacks on 500 unwanted insect species.(454) Many of the

introductions have been extremely successful. Table E26.6 (next page) shows the results

of some introductions, both successful and unsuccessful.

As one example, the long-snouted weevil has cleaned up milfoil and water hyacinth

worldwide.(255) Brazilian beetles have attacked the floating plant Salvinia molesta with

gusto all over Africa and Asia.(252) Klamath weed has been done in by European and

African beetles.(252) The phorid fly may be able to control the fire ant.(252)

Many insect and animal pests have natural predators they may have left behind.

Judicious use of these natural enemies (sometimes imported) can control the pests or

ameliorate the consequences of their presence. Understanding which virus attacks the

gypsy moth (Lymantria dispar) can help lead to control of the pest, because of

drawbacks in other methods of control. Attempts to control the gypsy moth is implicated

in the decline of the wild giant silk moth species of the American northeast such as

Hyalophora cecropia (which can grow to 15 cm across) because of the release of a

parasitic fly, Compsilura concinnata, to control the gypsy moth.(459) While the release of

the fly has now been stopped, fly populations remain at large.

TABLE E26.6.5

Invaders vs. Invaders

CommonName

ScientificName Origin Target Comments Ref.

Successful:beetle Hyperaspis

pantherinaorthezia scale(Orthezia insignis)

scale threatens St. Helenatree (Commidendrumrobustum)

130

ladybirdbeetle

Pseudo-scymnustsugae

Japan,China

woolly adelgid(Adelges tsugaeAnnand)

adelgid eat pine sap, pineslose needles, die; expectedcost in millions

455, a

phorid flies Pseudacteon S. America fire ant (Solenopsisinvicta)

near $1 billion per yearcosts, painful bites

456, a

spionidpolychaeteworm

Malacocerosfuligenosus

Medi-terranean

disturbed seabed inIreland

helps maintain coastalseabed

457

weevil Cyrtobagoussalviniae

Australia salvinia fern (Salviniamolesta)

weed now established offTexas, Louisiana

130

weevil Neochetinabruchi

central, S.America

water hyacinth(Eichornia crassipes)

beetles natural antagonistsof hyacinth, which causes

458, a

weevil Neochetinaeichhorniae

S. America water hyacinth(Eichornia crassipes)

extensive fouling, destroysecosystems

458, a

weevil Neohydro-nomus affinis

central, S.America

water lettuce (Pistiastratioles)

noxious weed in Australia 130

Food:giant tigershrimp

Penaeusmonodon

India food sold widely in United States a

Atlanticsalmon

Salmo salar N. Atlantic food farmed on Atlantic coasts ofU.S., Canada

a

Unsuccessful:SouthAmericancane toad

Bufomarinus

S. America gray backed canebeetle, frenchie beetle

in Australia, takes overecosystems

a

mynah Acridotherestristis

India sugar cane pestinsects

in Hawaii, one of 100 worstinvasive species

a

mongoose Herpestesjavanicus

India,Indonesia

rodents, rabbits,snakes

in Caribbean, takes overecosystems

381, a

Compsilura Compsiluraconcinnat

Europe gypsy moth(Lymantria dispar)

adverse effects onHyalophora cecropia

459, a

a Web searches conducted by author

Remember that jellyfish Mnemiopsis leidyi, the monster of the Black Sea that had an

“appetite is so great that it can double its size in a day”?(422) In the early 1990s, the mass

of M. leidyi in the Black Sea totaled an estimated 900 Mt, several times the annual oceanic

fish catch. Kideys et al. say, “By the late 1980s and early 1990s the pelagic ecosystem of

the Black Sea had become a dead-end gelatinous food-web.”(460)

In the late 1990s, M. leidyi invaded the Caspian Sea from the Black Sea, raising the specter

of a collapse of the Caspian Sea sturgeon fishery.(422) In fact, a study by nations

bordering the Caspian (Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan) pointed

out that, almost immediately, “sharp decreases were observed in the pelagic ... fishery of

Iran and Azerbaijan as well as of Russia.”(460) The study group identified an enemy of

this the monster jellyfish. It seems that another American east coast jellyfish, Beroe

ovata, had hitchhiked to the Black Sea in ballast about 1997. B. ovata eats other jellyfish

(including M. leidyi) in its home range, and immediately, the tide of M. leidyi began to

recede. The study group tested B. ovata in a bay of the Caspian and plan to release it into

the Caspian. It is expected that when it has eliminated the M. leidyi invasion, it will die

out from lack of food.(460)

However, it should be remembered that not all introductions pan out. Insects introduced

into the U.S. for weed control were really successful only 20% of the time, with some

positive control effects noted in a further 40%.(241) Perhaps only three or four of 210

insects and spiders introduced on purpose into the United States had a harmful impact:

the gypsy moth, the thistle weevil, and two insect parasitoids.(241,461)

The deer population of many states, out of balance with the environment because of the

eradication of wolves, could be controlled by judicious reimportation of the wolves to

reestablish the balance. Some recolonization of wolf-free areas has occurred.

Cassava, a South American crop that was introduced into Africa in the 1500s and now

feeds 200 million people in Africa, has been attacked by the mealy bug at a cost of $2

billion per year. A predator wasp, Epidinocarsis lopezi, was found in Paraguay; hundreds

of thousands of wasps per week were spread from planes, saving the crop.(462) In

addition, cassava is attacked by the cassava green mite, a less welcome import from Latin

America, which arrived in the 1970s. The problem was to find a way to control the mite

that did not involve expensive pesticides, as African farmers are generally poor. Most

enemy species of the green mite were unsuited for African climate, but eventually a mite

predator candidate from northeast Brazil, Typhlodromalus aripo, was identified.(463) The

predator only attacks the green mite, and has successfully reined in the mite’s

depredations.(463)

The good news: Natural and ecofriendly insecticides

Many plants produce natural insecticides. More than 10,000 compounds that protect

plants from insects are known.(141) Biological pesticides are gaining acceptance (see

Chapter 22). ClandoSan, made from crushed oyster shells, is used to control

nematodes.(464) An oil from the neem tree (Azadirachata indica) can protect plants

against 200 insects.(465) Grains can be protected for 10 weeks after spraying with

compounds from the neem. The tree is used to restore drought-stricken land in India.

Iowa farmers plant rye after the corn harvest. When the rye decomposes in winter, the

substances make a natural weed-killer.(466)

Many pests have been controlled through release of sterile insects. The California medfly

invasions and the screwfly have been dealt with that way. A new method of insect

population control has been proposed that involves releasing non-sterile insects that

possess a dominant lethal gene. The species do reproduce, but only for 3 to 5 generations.

It appears that the method will work, and may be cheaper than sterile insect release, since

the lethal gene has multiple opportunities to be transmitted.(467) There are similar

attempts to do in the pink cotton bollworm, Pectinophora gossypiella.(468)

The bitterwood tree from Costa Rica produces a natural insecticide. While the number of

local trees is too small to supply a world market, it suggests that research could identify

the source of the success of the tree and its wood in warding off insects.(37) Similarly, the

Spanish cedar has a volatile organic compound that repels insects.(469) If mahogany

plantations are attempted, it is certain that the known pests the mahogany shoot borers

(Hypsipyla grandella Zeller [American] and Hypsipyla robusta Moore [European]) would

have a field day. These two plants (there are probably others) could someday confer

insect resistance to mahogany trees through genetic engineering.(469)

Some parasitic members of the insect order Strepsiptera (“twisted wing,” a group of about

600 species) can enclose themselves in “bags” that the host’s immune system fails to

recognize as foreign.(470) One species, Stichotrema dallatorreanum Hofeneder, has been

used to control New Guinea long-horned grasshoppers [Segestidea novaeguineae

(Brancsik)] in New Guinea palm oil plantations. Apparently, S. dallatorreanum larvae

can penetrate the epidermis of the grasshopper, and when inside eat the organs.

Grasshoppers that survive are sterile.(470) Other grasshoppers can be parasitized as

well.(471)

The parasite has greater promise as well. Once known only from the males, females have

finally been identified using DNA, allowing the possibility of growing these parasites in

the lab and releasing them where needed. S. dallatorreanum can then be used to control

other susceptible pests, such as the pesky fire ant that invaded the American south.(472)

New natural pesticides using fungi, viruses, and bacteria, are replacing chemical pesticides.

A protozoan called Nosema locustae attacks only locusts.(473) An Australian wasp lays

eggs in grasshoppers.(473) The fungi are the most promising. The fungi of the group

Metarhizium flavorviride are assembled and concentrated; insects treated sicken and stop

eating within 2 days and die within 10 days.(473) All these developments promise hope

for the future.

The good news: Malaria and the mosquito

A new push to eradicate malaria is in the works because of past failures and the

consequences of inaction.(474) Malaria is a scourge killing and weakening millions of

people all over the world (a million dead and 300 million suffering malaria’s effects in

Africa alone each year). Malaria is concentrated in Africa, but also afflicts the Indian

subcontinent, southeast Asia, and Indonesia as a recently developed infection map

shows. (a) Smaller pockets exist in the Amazon region and its tributaries.(g)

The mosquito Anopheles gambia is parasitized by the actual cause of malaria,

Plasmodium falciparum, which is transferred from the mosquito to humans when the

mosquito sucks a person’s blood. The parasite hides in liver and spleen in humans, and

takes on a variety of forms, three different ones in the mosquito and another three in

humans.(475) Somehow this multiplicity of forms makes it impossible for the human

immune system to deal with the invader effectively, whence the tenaciousness of the

disease once a person has been infected.

Drugs have worked in the past to lessen symptoms, but the rise of resistant strains of P.

falciparum has made treatment much more difficult. The drug artemisinin is used in a

cocktail to treat sufferers who are live in areas of high resistance to the common

antimalarial drugs. It can get rid of malarial symptoms within three days’ time.(476)

Unfortunately, there is a supply problem—as resistant strains have expanded, more

countries are seeking to obtain it. The drug is derived from Chinese wormwood (Artemisia

annu), and an increase in supply lags demand by about 6 months because of the need for

new plants to be grown.(476) In addition, the drugs do not confer immunity to malaria,

they just treat the symptoms and reduce suffering. It seems that some out-of-the-box

thinking will be needed if we are ever to reduce the huge human toll of malaria.

There is always a different way to eliminate pests—build a better mosquito, for

instance.(477) Current malaria vaccines are effective short term for under half of people

vaccinated.(478) An entomologist at the University of California, Irvine, Anthony James,

has been trying to breed mosquitoes that cannot transmit the malaria parasite. If this can

be accomplished, the mosquito would still bite, and people would still scratch the bite,

but the mosquito could not transmit the disease.(477) Huge numbers of males of the new

species would be released in a specific region to breed with females, overwhelming the

native species in breeding success but not producing viable progeny, and then the new

species would be released in the region.

Taking a slightly different tack, Catteruccia et al. succeeded in making viable transgenic

malaria-less Anopheles stephensi mosquitoes.(479) Unfortunately, it appears that these

mosquitoes are unable to compete in the wild with native A. stephensi, so the problem is

still not solved.(480)

Another idea is to grow millions of mosquito parasites, irradiate them to prevent disease

from developing, and inject them into people. The irradiated parasite, called a sporozoite,

would provoke an immune response in its human host but otherwise do no harm.(478)

The failure of campaigns against mosquitoes, and the banning of DDT, have put many, in

the third world especially, at risk for the disease. Mosquitoes in any case have developed

resistance to insecticides.(481,482) For this reason alone it is important to know the genetic

code for the malaria mosquito, A. gambiae.(483)

The genes of A. gambiae have responded to human pressure by developing resistance to

the insecticides used for control.(482) Given the millions who are dying and at risk of

dying from malaria, it is important to use any weapon at our disposal that does not have

the serious side effects of DDT (and some countries still use DDT).

The DNA coding sequences of resistant and non-resistant mosquitoes was different at

just a few positions, allowing researchers to zero in on the change responsible for

insecticide resistance. It seems that a change in just one gene, the so-called ace-1 gene, a

gene coding for an enzyme (making acetyl-cholinesterase-1), was enough to lead to the

acquisition of resistance.(484) (This was a single point mutation and seems to have

occurred independently at least three times in A. gambiae and in Culex pipiens, the vector

for West Nile virus.) Weill et al. conclude that their work “opens the way to new

strategies for pest management. The development of new insecticides that can specifically

inhibit the G119S mutant form of acetyl-cholinesterase-1 will be crucial in overcoming the

spread of resistance.”(484)

Plasmodium falciparum has also been sequenced.(485,h) This could also allow

development of new ways to interrupt the transmission of malaria.(475) The genetic

information might be crucial in developing an effective and long-lasting vaccine. Some

progress in this direction has been made by Mueller et al., who find that “a safe and

effective, genetically attenuated whole-organism malaria vaccine is possible.”(i) The

researchers identified a gene that is necessary for a stage in the sporozoite’s development,

uis3. They tested immunization of rodents with uis3-deficient sporozoites, and found

that it “confers complete protection against infectious sporozoite challenge ... This

protection is sustained and stage specific.” Commentaries on the article(j) point to the

novelty of the work in that it is the first research that does not allow the Plasmodium

parasite (in mice, it is P. berghei) to develop in the host’s liver. The reproducibility of the

work is also important. It uses genetically attenuated sporozoites, which are now

possible to produce reliably because of the existence of the genetic map of P. falciparum

and other subspecies that have become available.(485,h)

Another development is the discovery of fungi that attack the host mosquitoes and thus

interfere with the transmission of the disease. Treatment with fungi shows promise

because the fungi attack the mosquitoes by contact; there is no necessity for repeated

exposure—once does the trick.

Blanford et al. used variants of Beauveria bassiana and Metarhizium anisopliae fungi.

These fungi that target the digestive tract (they are called fungal entomopathogens).(k) The

fungus can be sprayed on indoor fabrics or walls on which the mosquito might alight after

biting a human. The virulence was greatest with Beauveria bassiana, which is already

being sold as a biopesticide.(k) In the likely event that further research warrants, this

would make availability easier.

High (>80%) mortality was found in the model species used (the mosquito Anopheles

stephensi, the rodent malaria Plasmodium chabaudi) within 14 days (the time it takes for

the Plasmodium to develop infectiousness after exposure).(j) The researchers report that

“fungal exposure led to a reduction of transmission risk by a factor of about 80.”(j) The

infected mosquitoes were harmed in their development and maturation. This is a

spectacular result.

Scholte et al. used Metarhizium anisopliae fungus,(l) a constituent of a product that is

already sold in the United States to kill termites, which the EPA has determined is

harmless to people even if it is swallowed or taken into the lungs. The researchers hung

black cotton cloths impregnated with the fungus inside some homes in a small village in

Tanzania. They then collected mosquitoes from treated and control houses and kept them

until they died. Scholte et al. found that “fungus-infected A. gambiae s.l. had significantly

shorter life spans compared with those of noninfected mosquitoes.”(l) They modeled

malaria transmission to predict how the reduction in infectivity would affect the village

and find a 75% reduction in infections.(l) Here is another spectacular result, one of great

promise.

Problems exist with the fungal infection idea. For example, the spores seem to lose their

ability to infect mosquitoes within a few weeks.(m) If this problem can’t be dealt with,

the fungus would need to be sprayed repeatedly, which is unlikely to be possible in

remote, poor villages.(m) Another problem is that the fungi used kill other insects as well

as mosquitoes on contact.(n) Thus, the fungi could conceivably kill “good” insects.

Development of resistance in mosquitoes has been observed, and it is likely that that, too,

could occur with these fungi.(n) Michalakis and Renaud also point out that the fungus

could result in a behavioral change, one that would select mosquitoes who bit animals.

This could inflict economic losses, but such losses are surely preferable to the current

public health problems.(n) The most worrisome possibility is that the mosquito could

hasten development of infectiousness to circumvent the fungal infection.(n) After all the

worrying about things that could go wrong with the research results, Michalakis and

Renaud conclude that the research raises “the prospect of opening a new front in the war

on malaria. It is surely an approach worth pursuing.”

The good news: Natural and ecofriendly herbicides

Have you wanted to get rid of dandelions? Researchers have found that dandelions are

sensitive to the amount of potassium available. Fertilized lawns contain a lot of

potassium, necessitating a bumper crop of dandelions, or a run on a herbicide to get rid of

them. If a lawn must be fertilized, perhaps an application of ammonia would work better

than a full-spectrum fertilizer.(486)

The good news: Allelopathy

In addition to chemical signals from plant to plant to reduce the likelihood of attack as

exhibited by the invader Centaurea diffusa, plants have been found to use signals to

predators. For example, fall colors of leaves have been held to send a signal to predators

to pick on another tree.(487)

Volatile organic compounds are apparently being used by plants to send multiple

messages to herbivores wanting to graze—that the plant is defending itself, that it is under

attack already and no longer so appealing as a target, telling predators that herbivores are

available as prey, and telling herbivores that predators are in the vicinity waiting for them

to show up.(488)

The good news: The zebra mussel—a success?

Purdue University-Calumet researchers Cliff Chancey, a theoretical physicist, and

Matthew Ryan, a chemist, have found that zapping zebra mussels with low-frequency

electromagnetic waves in an aquarium kills them.(407,489) The waves interfere with the

mussels’ ability to process calcium.

The zebra mussels that are exposed to the radiation die within 40 days of their

exposure.(489) If the process can work in the real world, it may be able to beat back the

zebra mussel invasion.

The good news: Stemming invasions—what can be done?

One of the most problematic aspects of biological control is that some alien species

introduced to eliminate a pest did not do so, and that some alien species released to deal

with a specific threat instead attacked an alternative species (or set) and did not harm the

target species.(403) In other cases, the control attacked the proper target, but also attacked

other, desired, crops.(241,242,454)

The release of alien species is risky, but since it also has been very successful (as in the

case of M. leidyi), and since sometimes there seems no other alternative, how do we

minimize the chances of untoward consequences? Various strategies should be followed.

Alternative methods of control should be considered, if possible.(368) For example, we

need to make sure that the target is the only target.(380,490,491) This is easier if the species

is insect or arachnid than if it is a vertebrate (vertebrates tend to be more omnivorous and

so more dangerous to release, as was the red fox in Australia).(403,404) The species

introduced for control should not be a “generalist.”(461)

The best predictor of whether a species will be invasive is whether it has been invasive

elsewhere.(368,404) If it has, it should not be allowed in, because it is likely to become an

invader again.

In addition, risk assessment tools should be used wherever possible. Ecological niche

modeling, in which local conditions are matched with the species being considered for

introduction, is a useful tool.(492) An analysis of the danger of imports of Siberian timber

used modeling to consider what might happen. The import plans were dropped.(404) An

example of this is the analysis of the spread of Chinese tallow (Sapium sebiferum).(493)

The model identified places where the plant could possibly live, and it was test-grown in

those locations to check on the results.(493)

Modeling of the possible range of the Asian long horned beetle shows it can survive over

most of the country east of the Mississippi and in certain regions of the southwest.(492)

This information makes the efforts to keep the beetle out more important. Modeling can

also raise consciousness of the possible costs of invasions. One example is that of the

Japanese white-spotted citrus longhorn beetle (Anoplophora malasiaca) is not in America

at present, but the analysis shows it could invade major citrus-growing areas.(492) This

modeling is an important advance in deciding which species could be dangerous.

Assessment of various aspects (including those mentioned above, but including many

more attributes) should be checked off to make as sure as possible that the introduction

does not go awry.(404) Very important is the commitment to release just one control

organism rather than a host of control species. It is often when many species are released

that opportunities arise for spread from intended host to other species.(242) The point of

any biocontrol program must be to focus on the most useful species for the control

objective.

In addition, other alternatives should be considered seriously if the intended target is

similar to other non-target species. There is a history of food preferences changing in the

light of abundance. For example, the western corn rootworm beetle (it invaded in the

1860s) became resistant to the targeted insecticides in the 1960s and was controlled for

many years without pesticides by means of crop rotation.(494) The larva eat corn plant

roots. Adults lay eggs on corn plants in summer, and the larva emerge the next year to

munch on the roots. If they found soybeans, the idea was, they would starve to death.

And many did. However, apparently not all did. The few surviving beetles had developed

a taste for soybeans, too.(494) So it is clear that the presence of a relative or near relative

of the target species could undo the plan if the species is opportunistic enough.(242)

The safest introductions are those that release pathogens that affect only one host,(491)

parasitoids (species whose young are parasitic on the host species), or hyperparasitoids

(parasitoids of parasitoids).(490) Parasites are generally very host-specific. History shows

that no insect or spider species has been driven toward extinction by exotic invaders.(490)

Roughly one-sixth of the biocontrol programs using predators or parasitoids were

complete successes.(490) Refer to Table E26.6.5 for some successful invaders repulsed by

new invaders.

In addition, the geography of the region as a whole in which a release is contemplated

should be examined.(243) Since most invaders are unintended invaders rather than planned

ones, if a niche is available near the point of release, the species may well spread there,

even if that result is not intended. An example is the introduction of the caterpillar

Cactoblastis cactorum from Argentina into the Caribbean in 1957 to control a pest cactus

species. It did so, but hitchhiked into nearby Florida in 1989 and attacks native Florida

cacti.(242) Mexico also is home to many species of cactus, and dangerously close.(368)

Alert forethought might have averted the problem.

The most important step that the country could take would be to gather the

responsibility for checking for invading species in one bureaucracy. General categories

could be used to expedite decisions at borders, with lists of permitted species, prohibited

species, (the U.S. does have a blacklist of approximately 100 troublemakers),(417) and

those requiring further evaluation.(368) Technical Advisory Groups could be formed to

consider approval of the species that need more consideration.(242) Australia and New

Zealand have such a system based on the precautionary principle that is difficult for

intended invaders to penetrate: all plant species are barred unless they have been

determined to be safe.(404,417) Clearly a system having a central theme is more resistant to

invaders than a catch as catch can system and should be adopted.

The real danger remains unintentional introduction, common in the past but much easier

now.(251) For example, West Nile virus was brought into the United States in a mosquito

who hitchhiked in a jetliner. Only 11% of introduced insects were brought in on purpose.

On the other hand, 40% of the exotic fish were brought in on purpose.(404) How we

ultimately deal with this problem remains for the future to determine.

References in addition to those listed for this chapter are shown in red in the text, and

listed below:

a. R. E. Gozlan, S. St-Hilaire, S. W. Feist, P. Martin, and M. L.Kent, “Disease threat toEuropean fish,“ Nature 435, 1046 (2005).

b. T. Henry, “NW Ohio said key to keeping U.S. pest-free,” The Toledo Blade, 21 April2005

c. T. Henry, “Multistate tree-skinning effort aims to close beetle’s gateways,” The ToledoBlade, 18 May 2005.

d. T. Henry, “Insecticides offer hope for control of ash borer,” The Toledo Blade, 7 April2005.

e. T. Henry, “U.S. plans for worst-case ash scenario,” The Toledo Blade, 22 May 2005.

f. M. Taugher, “Alien species infest waters of Bay, Delta,” The Contra Costa Times, 22

June 2005.

g. R. W. Snow, C. A. Guerra, A. M. Noor, H. Y. Myint, and S. I. Hay, “The globaldistribution of clinical episodes of Plasmodium falciparum malaria,” Nature 434, 214(2005).

h. N. Hall, M. Karras, J. D. Raine, J. M. Carlton, T. W. A. Kooij, M. Berriman, L.Florens, C. S. Janssen, A. Pain, G. K. Christophides, K. James, K. Rutherford, B. Harris,D. Harris, C. Churcher, M. A. Quail, D. Ormond, J. Doggett, H. E. Trueman, J.Mendoza, S. L. Bidwell, M.-A. Rajandream, D. J. Carucci, J. R. Yates, III, F. C. Kafatos,C. J. Janse, B. Barrell, C. M. R. Turner, A. P. Waters, and R. E. Sinden, “Acomprehensive survey of the Plasmodium life cycle by genomic, transcriptomic, andproteomic analyses,” Science 307, 82 (2005).

i. A.-K. Mueller, M. Labaied, S. H. I. Kappe, K. Matuschewski, “Genetically modifiedPlasmodium parasites as a protective experimental malaria vaccine,” Nature 433, 164(2005).

j. R. Ménard, “Knockout malaria vaccine?,” Nature 433, 113 (2005). A. P. Waters, M. M.Mota, M. R. van Dijk, and C. J. Janse, “Malaria vaccines: back to the future?,” Science307, 528 (2005).

k. C. S. Blanford, B. H. K. Chan, N. Jenkins, D. Sim, R. J. Turner, A. F. Read, and M. B.Thomas, “Fungal pathogen reduces potential for malaria transmission,” Science 308, 1638(2005).

l. E.-J. Scholte, K. Ng'habi, J. Kihonda, W. Takken, K. Paaijmans, S. Abdulla, G. F.Killeen, and B. G. J. Knols, “An entomopathogenic fungus for control of adult Africanmalaria mosquitoes,” Science 308, 1641 (2005).

m. M. Enserink, “Mosquito-killing fungi may join the battle against malaria,” Science 308,1531 (2005).

n. Y. Michalakis and F. Renaud, “Fungal allies enlisted,” Nature 435, 892 (2005).