1 - Hurdles to Herbivory Flashcards
Compensatory feeding
eating large amounts of N-poor tissue to compensate for low value
ECI
efficiency of conversion of ingested food…
Endophagy
feeding inside plant tissues
Filter chamber
modified gut allows sucking insects to concentrate N from dilute plant sap
excess water secreted as honeydew!
Prolegs
fleshy abdominal legs of some larvae
Microbial gut symbionts
help digestibility, much like ruminant animals
Polyphagous
can feed on various types of unrelated plants (generalists)
locust, beetle
Oligophagous
feed on restricted set of plants (related, families)
CO potato beetle (Solanaceae), cabbage looper (Cruciferaceae)
Monophagous
feeds on only one species (or genus) of plant (specialist)
Secondary plant chemicals
compounds not universally found in higher plants, restricted to certain taxa or in higher amounts than others
no apparent role in primary plant metabolism
hundreds of thousands
Only 1/3 of insect orders can feed on plants. Why?
have not succeeded in overcoming southwood’s hurdles… or no need to
According to T.R.E. Southwood, what are the three major hurdles to herbivory?
- attachment
- desiccation
- nutrition
Adaptations to overcome desiccation? (HoH2)
drinking
wax layer of exoskeleton
close spiracles
recycle fluids
dry fecal matter
endophagy
eggs. ..
- bury in soil/insert into plant
Caterpillar adaptations that boast so much success?
prolegs ?
Why is N a limiting element in diet of plant-feeding insects?
limiting element in all herbivores!
higher N = more efficient conversion of carbs for faster growth
How do dietary requirements for insects vary from vertebrates?
insects need to imbibe sterols (cannot produce)
Why must insects obtain sterol(s)?
cannot synthesize themselves…
component of cell membranes, precursors of synthesis hormones
What is ‘puddling’ by butterflies? What limiting element are they after?
clinging to wet soil, acquires sodium as its leached out
According to Fraenkel, what is the raison d’etre (reason for being) of plant secondary chemicals? Why was this controversial in 1959?
defense system against insects and other herbivores… now guide specialists to food
“Green World Hypothesis”
Plants successfully cover the Earth and herbivores rarely demolish their food supply, in natural systems… because herbivores are limited by PREDATORS, PARASITES, and DISEASES.
Why is the ‘Green World Hypothesis’ an oversimplification?
many other factors determine populations of insects
“Dual Discrimination Hypothesis”
Kennedy
secondary chem AND nutrients are cues…
chem: recognition and range
nutrient: feeding site (tissue)
T.R.E. (Sir Richard) Southwood
determined hurdles to herbivory
Gottfried Fraenkel
raison d’etre of secondary plant chemicals
