Lectures 20 and 21 Root-feeding insects

Weevils

Rostrum

Rostrum

Three importantexamples of theroot weevil complex.

Black vine weevil Otiorhyncus sulcatus

Strawberry root weevil O. ovatus

Woods weevil Sciopithes obscurus

(1) grow strong varieties ofstrawberries,

(2) allow poultry to run in thestrawberry patches

(3) trap adults under boards orstraw

(4) spray, if you feel you must, witharsenate of lead, two pounds of powder to 100 gallons of water

(5) clean up and burn old leaves andrefuse in the fields or gardens

A 1926 version of what we would call, IPM!

The black vine weevil

Typical leaf damage caused byroot weevils. Females have tofeed on leaves to mature theirovaries.

More Adult WeevilDamage

Weevils beforefeeding on foliage

Weevils afterfeeding on foliage

The root weevils are common to the northern half of U.S. and southern half of Canada.

The most destructive form is the larval form as grubs feed on roots and lower stems. There are hundreds of hosts, a few would be: yews, rhododendrons, strawberries, many green house plants and Douglas-firs in nurseries.

• The flightless, parthenogenic females hide under boards, litter, and trash during the day.

•At night they climb plants and feed on leaves. Egg laying occurs during early summer through July. Eggs are found at the base of host plants. After hatching the grubs move into the soil and feed on roots.

• Later instars move to the root crown, feed on the stem and pupate just under the soil.

• Adults then emerge and continue to feed during warm fall and winter days. Adults are long lived, often more than 3-yrs.

Grubs feedingon roots ofrhododendrons

Leaf notching

Sharon Collman picking weevils outof nursery containers

Larvae found in containers

Intense root andstem damagecaused by grubs

Black vine weevil

Severe damage causedby root-feeding weevilgrubs

Damage by root weevils onrhododendron in PNW

Pest mgt. -- Adult controlshould begin when adultsemerge in May-June. Larvalcontrol is done in autumn.

Azadirachtinbifenthrincyfluthrinacephatebeneficial nematodesBeauvaria bassiana

Plant weevil-resistant Rhododendrons: R. edgeworthii R. leuteum R. mergeratum R. trichostomum And others.•

2 0 0 4

The Scarabaeidae: Scavengers and Herbivores

Dung beetle -- scavenger saprophage

Leaf chafers -- herbivore

A good illustration on theimportance of saprophagousinsects is what happened inAustralia. Cattle were introducedinto vast areas of northernAustralia, an area with few saprophagous insects thatfed on dung.

A suite of saprophages were introduced into Northern Australia to recycle the large amounts of accumulatingcattle dung. Introduction of these beetles was a resounding success.

Processing bythe beetles wasbeneficial to pasture growth.

Dung rollers are fascinating to watch

Some scarabs are metallic coloredand used in jewelry

The root and leaf-feeding scarabs (the leaf chafers)severely damage grasses, crops and nurseries.

The ten-lined June beetle is a scarab.• Larvae feed on roots •Adults feed on leaves of hardwoods

Leaf chafer adults feed on foliage, while the grubs feed on roots

Leaf chafers include the May beetle, June beetle,Japanese beetle, rain beetle and others. The onesdestroying lawns belong to the Phyllophaga spp.

In the PNW these are the June beetles that includeseveral species.

Adults are nocturnal andattracted to lights. June beetlesemerge from pupal cells in thesoil during April- June (dependson the weather). Adults feed onfoliage of birch, elm, ash, maples,and other hardwoods.

Later each female lays 150-200 eggs inthe soil and larvae feed on rootsof turf or pasture grass.

The population overwinters as larvae and the last instar constructsa pupal cell.

White grubs -- Larvae are variable in size with robust, cream-colored bodiesand black heads. Grubs feed on roots. Turf damage generally appearsas patches of dead turf that are not anchored to the soil. Symptoms mayoccur from spring through fall.

Control -- beneficial nematodes, imidacloprid

Bacillus popillae MACH 2 Other insecticides

How -- Treat when grubs are active near the soil surface. irrigate treated area immediately after application.

2 0 0 4

Another Root PestThe European cranefly whose larvae feed

on stems, root crowns and roots of grasses

The Crane Flies: Tipulidae

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More on the tipulids

Leather jackets

C.P. AlexanderAlexander, born 1889 and died 1981. During his career he described almost 11,000 species of Tipulidae and he wrote 1017 articles, 20,000 pages of books, and produced 15,000 of his own illustrations. His contribution to entomology is immense.

The Tipulidae – crane flies

J. R. Vockeroth

Recipient of the 2003 C.P. AlexanderAward by the International Societyof Dipterology

The European crane fly: Tipula paludosa Alex., a turf pest

Leatherjackets feeingon roots of turf

European craneflyLarvae hatch in the late summer and feed onroots, root crowns and shoots through winter and into spring, causing turf damage anytimebetween Jan-May.

Affected lawns often thin out severely in early spring when normal turf starts vigorous growth. Starlings and other birds are attractedto infested lawns and may cause accelerated turf damage as they search for larvae.

Cranefly larvae can be controlled easily withrecommended insecticides. Monitor turfstarting in Jan, and consider treating whenlarval populations reach 25+ per sq. ft or when damage is apparent.

European crane flyin Laurelhurst

Leather jackets

Another Root-feeding Insect: Sod WebwormBelong to the moth family Pyralidae whichinclude the snout moths.

Sod webworm damage

Damage most common on wet

parts of the lawn

Sod Webworms (Chrysoteucia topiara)

Larvae feed at bases of grass blades and onnew tender roots.

You can look at the base of the dying sod and observe the chopped-off blades

Damage begins as relatively small, irregular spots of dead and dying grass. During sod webworm outbreaks the spots coalesce and major damage ensues.

May-June (Late Spring)

• See erratic flying moths hovering over your lawn at dusk;• Erratic flying moths attracted to lights;• Lay eggs in slight lawn irregularities – aeration holes;

Summer

• Larvae feed on grass blades and succulent roots:

Fall & Winter

• Pupate in early fall and overwinter as pupae

Late Spring

• Next adult generation emerges

Remember we said that the sod webworm prefers a wet site? What site is wetter than cranberry bogs?

When this insect, Chrysoteucia topiara, is found killing cranberries, it’s called the cranberry girdler.

When this insect girdles Douglas-fir seedlings in nurseries it’s still called the cranberry girdler. And it’s a serious pest!

Management of cranberry girdler: Douglas-fir seedlings

• Damage – Larvae feed on the roots and lower stem of seedlings.

• Damage occurs when seedlings are grown or planted near to grass fields, which are the primary habitats for this insect.

• Diagnosis – On the lower stem and seedling taproot look for patches where bark and cortex have been removed.

• Biology:

Management of the cranberry girdler attacks on Douglas-fir seedlings

• In nurseries, avoid using cover crops that would provide host material for the insect. Cultivate or apply herbicides to non-nursery areas to control grasses and weeds.

• Monitor the population with pheromone traps:

• The pheromone traps also will be used to time application of pesticides.

• Mach-2 or other product used to control root-feeding insects should be applied:

* 3-5 weeks after the start of moth flight to reduce seedling damage (the target would be early instars).

* Additional pesticide treatment may be made in late summer to get the last instar before pupation.

Cranberry girdlers

They girdle and killDouglas-firseedlings.