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
John S. Kennedy
Dual Discrimination Hypothesis
how many insect orders can feed on plants?
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What are ‘top-down’ factors? name some associated with the Green World Hypothesis
consumer limiting factors (not resources, which are bottom up)
predators, parasites, diseases
Adaptations to overcome attachment (HoH1)?
structural mods
- tarsi
- prolegs & crochets
- stylet mouthparts
secretions
- scale insects
- reversible rectal organs…
crochets
hooks on feet (like velcro)
Adaptations to overcome nutrition (HoH3)?
compensatory eating
selective feeding
prolonged development
digestive adaptations
- gut symbionts to help with cellulose
nutrient requirements?
water
carbs: energy
amino acids: protein synth
lipids
fatty acids
vitamins (except D, no Ca skeleton!)
mineral nutrients:
- Na, nerve/muscle function (low in plant tissues)
- Fe, Mg, Zn other trace, cofactors in enzymes and cellular resp, harden parts (mandibles)
STEROLS: cell wall and hormone precursor
sequestered chemicals… defense or precursors
% specialists?
80%!
what is the relationship between nitrogen content of plant tissues and ECI by insects?
newer/specialized tissues are more N rich… insects have to eat less
older tissue less rich, need to eat more (compensatory)
