Manipulation of Tritrophic Interactions for IPM

Tri-trophic Interaction

Plants

Herbivores

Predator/parasitoids

Plants Interact With the Third Plants Interact With the Third Trophic LevelTrophic Level

ChemicallyChemically MorphologicallyMorphologically

Multi-trophic interactions

Plants

Herbivores

Predator/parasitoids

Hyperparasitoid

The Slow Growth High Mortality Hypothesis

• Feeding on sub-optimal food produces an increase in insect herbivore developmental time.

• Increased developmental time in herbivores may increase vulnerability to natural enemies

The Slow-Growth-High-Mortality Hypothesis

• Prolonged larval development of herbivores results in greater vulnerability and thus greater mortality due to natural enemies.

(Clancy and Price 1987).

Tests Have Produced Mixed Results

• Support:

- Free feeding herbivores.

- Feeding on same or related plant species.

• Fail:

- Concealed feeding herbivores.

- Feeding on unrelated plant species.

G.lineolaG.lineola

- Predators attack more on S.dasyclados

- Develop longer on S.sasyclados

P.rapae

M.disstria

- Develop longer on low N collards

- Predators attack more on low N collards

- Develop longer on late budbreaks

- Predators attack more on late budtbreaks

Studies Supporting the Hypothesis

Which Natural Enemies Have Been Considered to Test the

Hypothesis?

• Suite of predators.

• Single parasitoid species.

• Parasitoid community.

Acer negundo

Salix nigraSalix nigra

Orgyia leucostigmaOrgyia leucostigma

Experimental Protocol

• Rear O. leucostigma on willow and box elder.

• Measure development time and adult mass on willow and box elder.

• Use 7-year data base to determine percent parasitism of O.leucostigma on willow and box elder.

O. leucostigma developed faster on willow

28

29

30

31

32

33

34

Willow Box Elder

Diet

Ave

rag

e d

eve

lop

me

nt

tim

e (

in d

ays)

A

BP<0.0001

Female O.leucostigma on willow were heavier than on box elder.

0

50

100

150

200

250

300

350

Willow Box Elder

Diet

Wei

gh

t (m

g)

B

A

CC

F F

M M

a a

b

c

Braconidae Cotesia delicata 19.35 80.65

Cotesia melanoscela 6.25 93.75

Cotesia sp 18.75 81.25

Meteorus hyphantriae 33.33 66.67

Meteorus sp 38.89 61.11

Ichneumonidae Casinaria limenitidis 50.00 50.00

Casinaria sp 85.71 14.29

Hyposoter fugitivus 50.00 50.00

Eulophidae Elachertus sp 33.33 66.67

Tachinidae Carcelia amplexa 50.00 50.00

TOTAL 11 30.00 70.00

Braconidae Cotesia delicata 19.35 80.65

Cotesia melanoscela 6.25 93.75

Cotesia sp 18.75 81.25

Meteorus hyphantriae 33.33 66.67

Meteorus sp 38.89 61.11

Ichneumonidae Casinaria limenitidis 50.00 50.00

Casinaria sp 85.71 14.29

Hyposoter fugitivus 50.00 50.00

Eulophidae Elachertus sp 33.33 66.67

Tachinidae Carcelia amplexa 50.00 50.00

TOTAL 11 30.00 70.00

FamilyFamily Parasitoid speciesParasitoid speciesOverall percent parasitism onOverall percent parasitism on

Box elderBox elder WillowWillow

1. X2 = 11.83; P<0.001

Percent Parasitism of Percent Parasitism of O.leucostigmaO.leucostigma on two tree species on two tree species

In Summary

• O. leucostigma developed faster in willow than in box elder.

• Overall parasitism in O.leucostigma was greater in willow than in box elder.

Conclusion

• The slow-growth-high-mortality hypothesis does not hold for O. leucostigma and its parasitoid community.

Conclusion

On a free feeding herbivore feeding on On a free feeding herbivore feeding on unrelated species.unrelated species.

• Support:

- One parasitoid species considered.

• Fail:

- A community of parasitoids considered.

Conclusion

• The effect of host plant quality on individual species of natural enemies might differ significantly from the effect of host plant quality on the natural enemy community.

Differential susceptibility of herbivores to natural enemies