Insect Damagegrasshopper

potato beetle

spider mites

aphids

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 lifetime

ChrysophidsSyrphids Coccinellids

Biological Control

Syrphid : Aphid Ratios

• Temperature dependent aphid population growth

• Starvation of syrphids

1:1701:70

1989

0

10

20

30

0 2 4 6 8 10 12

Days after Release

Ap

hid

s

1991

0

10

20

30

0 2 4 6 8 10 12

Days after Release

Ap

hid

s

N-isoclines for different growth rates of aphid population

Number of Predators

Number of Prey

1.02

1.01

2.72

1.06

3.19

(Tenhumberg, Environ Entomol 1995)

How many predators do we need?

• Aphid density• Aphid population growth rate

– Temperature– Host plant (nutritional values)

• Predator species– How much do they eat– Temperature– Nutritional value of aphid– How quickly do the find and eat the prey

Temperature

Temp [oC] Larval Adult Fecundity intrinicmort. [%] lifespan [d] growth rate

10 3.5 20 44 1.015 8 22 53 1.920 13 19 61 0.425 18.6 12 4 0.030 100 - -

Metopolophium dirhodum (Dean 1974)

Easy estimatesMaximum number of aphids consumed during larval phase

Episyrphus balteatus

Aphid species Size Temp [oC] No aphidsSitobion avenae 3rd 17 140 Ankersmit et al (1986)Metopolophium dirhodum 3rd 14 1113 Tenhumberg (1992)Metopolophium dirhodum 3rd 17 1041 Tenhumberg (1992)Metopolophium dirhodum 3rd 20 886 Tenhumberg (1992)Metopolophium dirhodum 3rd 22 658 Tenhumberg (1992)Aphis fabae medium 15 553 Wahbi (1997)Aphis fabae medium 20 407 Wahbi (1997)Aphis fabae medium 23 1322 Wahbi (1997)

Source

Model System

Vicia faba

Acyrthosiphon pisum(hemimetabolous)

Hippodamia convergens(holometabolous)

Aphids• 4,400 species of small insects

– 250 species are serious pests• Aphids 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 Drepanosiphidae

70% of species

Aphid Feeding

• Specialization– Monophagous:

feeding only on 1 species of plant– Polyphagous:

feed on hundreds of plant species • How do they feed

– Passive 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 thirsty

• Virus transmission

Plant Tissues

• Xylem:conducts water and dissolved minerals from the roots to all the other parts of the plant.

• Phloem– Sieve 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.

Honeydew

Excretion 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.

http://en.wikipedia.org/wiki/Aphid

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 movement– death of the host plant – danger – end of season– overpopulation

• Short distance dispersal: 1.6 to 3.2 km per hour • Long distance dispersal: >400 km in 9 hours

– Fly upwards to get above the planetary boundary layer (1000m above sea level) and are carried by the low level jet streams

Winged forms (alatae) appear

Reproduction:

• Thelytokous parthenogenesis:Obligate parthenogenesis where females give birth only to female offspring

• Short 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 Cycles

• Alteration of sexual and asexual generations– Holocyclic

• Species that produce both sexual and asexual morphs • Cyclical parthenogenesis: Many generations of asexual

(parthenogenetic) reproduction (all females), followed by single generation of sexual reproduction

– Anholocyclic• Species 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 Species

• Asexual and sexual morphs are produced at different times of the year.

• Males are present only in one part of the life cycle.

Viviparous females(winged and unwinged)

Oviparous female(unwinged)

Male(winged and unwinged)

Egg(typically

overwintering)

Fundatrix(usually unwinged)

Anholocyclic Species

• No sexual males and females • No direct descendants of the sexual morphs,

namely the egg and the fundatrix. • Often no primary host.

Viviparous females(winged and unwinged)

Viviparous females(usually overwinter asapterae or nymphs)

Host Alternation

• Autoecious: single host plant• Heteroecious: alternating between

host plants

Primary host:Shrub or tree

Secondary host:Herbaceous plant

Acyrthosiphon pisum• Common name: pea aphid• Pink 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 are• Reproductive rates of both morphs are the

same• Aphid defensive behaviour of both morphs

is the same.

A. pisum Life Cycle

Acyrthosiphon pisum

• DistributionThroughout the U.S. and Canada

• Host Plants Sweet peas, sweet clover, alfalfa, and some leguminous weeds. Vetch and crimson clover are important overwintering hosts

Plant Damage• Extract 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

Vicia faba

Lady Beetles(Coleoptera: Coccinellidae)

• Over 450 species are found in North America. Some are native and some have been introduced from other countries.

• Food:– aphids– mites, small insects, and insect eggs– plants

(Mexican bean beetle, Epilachna varivestis, squash beetle, Epilachna borealis)

– Low food availability• pollen, nectar• cannibalistic

Aposematism

• Warning colors: – Most predators associate bright colors

(especially orange and black or yellow and black) with poison and other unpleasant properties.

• Toxin– toxic 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 Coccinellids

• Overwintering– often in aggregations

along hedgerows, beneath leaf litter, under rocks and bark, and in other protected places including buildings.

• Migration– In 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 fall• Consumption• Cannibalism• Fecundity (no. eggs) and fertility

(fertile eggs)• Migration• Pesticide application

References

• Dixon, A.F.G (1998): Aphid Ecology, Chapman and Hall, London, UK, pp.300

• Hodek, I. and A. Honek (1996): Ecology of Coccinellidae, Kluwer Academic Publishers, The Netherlands, Dordrecht, pp. 464

Lab overview

• Parameter estimation for aphid model– Developmental time– Survival– Fecundity

• Testing predicted aphid population growth rate

• How much do predators eat?– Maximum aphid consumption at different

developmental stages

Aphid Experiments

Model

1 2 3 4 5 6 7 8 9 10 12 14 16 18 20

010

020

030

040

050

060

0

Time [days]

Tot

al P

opul

atio

n

Asymptotic GrowthMaximum Transient

H. convergens

• Access food – Larva:

> 20 aphids/day– Adults:

> 50 aphids/day