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DESCRIPTIONInsect Damage. grasshopper. spider mites. potato beetle. aphids. This wasp is laying its egg inside an aphid where its young will develop. Parasitoid larvae develop on or inside a host, killing it as they mature. They emerge as adults and continue the cycle. Parasitoids. - PowerPoint PPT Presentation
Insect Damagegrasshopperpotato beetlespider mitesaphids
Parasitoids This wasp is laying its egg inside an aphid where its young will develop. Parasitoid larvae develop on or inside a host, killing it as they mature. They emerge as adults and continue the cycle.
PredatorsA predator consumes many prey during its lifetimeChrysophidsSyrphidsCoccinellids
Syrphid : Aphid RatiosTemperature dependent aphid population growthStarvation of syrphids
N-isoclines for different growth rates of aphid populationNumber of PredatorsNumber of Prey(Tenhumberg, Environ Entomol 1995)
How many predators do we need?Aphid densityAphid population growth rateTemperatureHost plant (nutritional values)Predator speciesHow much do they eatTemperatureNutritional value of aphidHow quickly do the find and eat the prey
TemperatureMetopolophium dirhodum (Dean 1974)
Easy estimatesMaximum number of aphids consumed during larval phase Episyrphus balteatus
Model SystemVicia fabaAcyrthosiphon pisum(hemimetabolous)Hippodamia convergens(holometabolous)
Aphids4,400 species of small insects 250 species are serious pestsAphids are divided up into 10 families all of which have been extant for 50 - 70 million years
Superfamily Aphidoidea Pemphigidae Anoeciidae Hormaphididae Mindaridae Thelaxidae Lachnidae Phloeomyzidae Greenideidae Aphididae Drepanosiphidae70% of species
Aphid FeedingSpecializationMonophagous: feeding only on 1 species of plantPolyphagous: feed on hundreds of plant species How do they feedPassive feeding on sap of phloem vessels: This sap being kept under high pressure, once a phloem vessel is punctured, it is forced into the food canal. Active feeding (sucking) from xylem vessels when thirstyVirus transmission
Plant TissuesXylem: conducts water and dissolved minerals from the roots to all the other parts of the plant. PhloemSieve elements conducts the products of photosynthesis - sugars and amino acids - from the place where they are manufactured (a "source"), e.g., leaves, to the places ("sinks") where they are consumed or stored; Companion cells move sugars and amino acids into and out of the sieve elements.
HoneydewExcretion of sticky substance known as "honeydew" which usually becomes black with sooty mold. Aphid honeydew is rich on carbohydrates (like melezitose), of which the aphids ingest an excess, being phloem-feeders.Some species of ants "farm" aphids, protecting them on the plant they eat, and eating the honeydew that the aphids secrete; this is a mutualistic relationship.
Migration and Dispersal Most of the time aphids do not have wings, and in general they move very little, and life consists of feeding and giving birth.What stimulates movementdeath of the host plant danger end of seasonoverpopulationShort distance dispersal: 1.6 to 3.2 km per hour Long distance dispersal: >400 km in 9 hoursFly upwards to get above the planetary boundary layer (1000m above sea level) and are carried by the low level jet streamsWinged forms (alatae) appear
Reproduction:Thelytokous parthenogenesis: Obligate parthenogenesis where females give birth only to female offspringShort generation time (about 10 days on average)Telescoping of generations: Grandaughters begin developing directly within the daughters which are themselves not yet born
Aphid Life CyclesAlteration of sexual and asexual generationsHolocyclicSpecies that produce both sexual and asexual morphs Cyclical parthenogenesis: Many generations of asexual (parthenogenetic) reproduction (all females), followed by single generation of sexual reproductionAnholocyclicSpecies that produce only asexual morphs Although many species are either holocyclic or anholocyclic, many other species possess both holocylic and anholocyclic populations Host plant alternation
Holocyclic SpeciesAsexual and sexual morphs are produced at different times of the year. Males are present only in one part of the life cycle.
Anholocyclic SpeciesNo sexual males and females No direct descendants of the sexual morphs, namely the egg and the fundatrix. Often no primary host.
Host AlternationAutoecious: single host plantHeteroecious: alternating between host plantsPrimary host:Shrub or treeSecondary host:Herbaceous plant
Acyrthosiphon pisumCommon name: pea aphidPink and green genotypes (polymorphism)Green morphs suffer higher rates of parasitism than red morphs Red morphs are more likely to be preyed on by predators than green morphs areReproductive rates of both morphs are the sameAphid defensive behaviour of both morphs is the same.
A. pisum Life Cycle
Acyrthosiphon pisumDistributionThroughout the U.S. and CanadaHost Plants Sweet peas, sweet clover, alfalfa, and some leguminous weeds. Vetch and crimson clover are important overwintering hosts
Plant DamageExtract sap from terminal leaves and stems Feed on pods causing them to curl, shrink, and partially fill. Feeding can result in deformation, wilting, or plant death Plants less than 15 cm (6 in) high are easily killed by a few aphids, whereas larger plants are only slightly damaged. Coated with shiny honeydew Virus transmission, e.g. pea enation mosaic and yellow bean mosaic viruses. Heavy infestations of pea aphid have caused chlorosis (yellowing) and wilting of plants in this plot of susceptible alfalfa Bean pod damage
Lady Beetles(Coleoptera: Coccinellidae)Over 450 species are found in North America. Some are native and some have been introduced from other countries.Food:aphidsmites, small insects, and insect eggsplants (Mexican bean beetle, Epilachna varivestis, squash beetle, Epilachna borealis)Low food availabilitypollen, nectarcannibalistic
AposematismWarning colors: Most predators associate bright colors (especially orange and black or yellow and black) with poison and other unpleasant properties. Toxintoxic to smaller predators, such as lizards and small birds; Adults are able to reflex-bleed from their leg joints, releasing their oily yellow toxin with a strong repellent smell.
Adult CoccinellidsOverwinteringoften in aggregations along hedgerows, beneath leaf litter, under rocks and bark, and in other protected places including buildings. MigrationIn spring, the adults disperse in search of prey and suitable egg laying sites.
Hippodamia convergens(1-2 generations / year)
Predation efficiency(H. convergens)Activity period: late spring-early fallConsumptionCannibalismFecundity (no. eggs) and fertility (fertile eggs)MigrationPesticide application
ReferencesDixon, A.F.G (1998): Aphid Ecology, Chapman and Hall, London, UK, pp.300Hodek, I. and A. Honek (1996): Ecology of Coccinellidae, Kluwer Academic Publishers, The Netherlands, Dordrecht, pp. 464
Lab overviewParameter estimation for aphid modelDevelopmental timeSurvivalFecundityTesting predicted aphid population growth rateHow much do predators eat?Maximum aphid consumption at different developmental stages
H. convergensAccess food Larva: > 20 aphids/dayAdults: > 50 aphids/day
*Developmental time*Consumption per day did not vary much*Dinosaurs went extinct 65 million years ago*Cambium: dividing celsPith: core of the stem of most plants Cortex: the outer portion of the stem or root of a plant *ephemeral resources = lasting a short timeThelytokous: Reproduction that is exclusively female with no male contribution to the young. *Males are produced de novo by parthenogenetic females, usually only in the autumn. Aphids can accomplish this feat because they have an XO sex determining mechanism. Individuals with two sex chromosomes (XX) develop into females, whereas individuals with one X chromosome (XO) develop into males. To produce a male, a special "mini-meiosis", which involves only the X-chromosomes, eliminates one of the X chromosomes during oogenesis. Blackman (1974, 1987) provides a detailed review of the phenomenon.*Primary host = ancestral" host *Coccinellids lay extra infertile eggs with the fertile eggs. These appear to larvae when they hatch. The ratio of infertile to fertile eggs increases as with scarcity of food at the time of egg laying. (Perry & Roitberg, 2005)*20-1000 eggs, hibernation after mating