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Announcements• Field trips coming up

– Galbreath Apr 26• Meet at parking lot at 8:00 a.m.• Return by 5:00 p.m.• Bring collecting equipment• Also bring food and water and mosquitorepellent

– Pepperwood May 4

• Deadlines– Insect collection May 14– Field Journal May 12

Secondary Compounds• Behavioral Effects

– Repellant– Inhibit oviposition or feeding

• Physiological Effects: Toxicity– Qualitative

• Small molecular weight, poisonous compounds• Usually found in ‘unapparent’ plants• Specialist herbivores develop

detozification

– Quantitative• Large molecular weight digestibility

reducers (e.g. tannins)• Found in large ‘apparent’ plants• Tend to support more generalist herbivores

Other Determinants of Diet– Host plant stress

•Plant defenses weakened

•Makes plant more favorable

– Resource rich plants•Nitrogen needed to make proteins•Nitrogen levels much lower in plantsthan animals

•Vigorously growing plants may providemore nutrient rich food

Insect Plant Interactions

• Evolution– 50% of all insects feed on plants– This great diversification of insects

occurred only 60 million yrs ago.– Why?

Coevolution– Evolutionary change (genetic change) in

one species causes evolutionary changein another

– Hot topic in evolutionary biology• Predators vs prey- insect-insect interactions• Hosts vs parasites

– parasitoids and host insects– Bacteria versus host insect

• Mimicry- Batesian and Mullerian• Mutualisms- plants and pollinators

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Coevolution

• Pairwise coevolution– Evolution of traits in one species cause

changes in another– These changes in the other species cause

changes in the first• Reciprocal interactions proposed• May cause speciation

Coevolution

• Diffuse coevolution– Reciprocal evolutionary change among

groups of species rather than specificpairs

– Specificity of response not as important

Diffuse coevolution in oceansRole of plant chemicals

• Plants possess many compounds notneeded for primary metabolism(secondary metabolites)

• These are often repellent or toxic toherbivores

• Perhaps they evolved in response toinsect herbivory

Cost of 2ndary metaboliteproduction

• Example of nicotinebiosynthesis

• Requires severalbiosynthetic steps

• Requires nitrogen• Nicotine concentration

increases after herbivoredamage (induced)

• Benefit: reduces herbivory• Cost: Flower production

reduced by nicotineinduction

Ehrlich and Raven hypothesis• Plants evolve new 2ndary metabolites in

response to herbivores• Plants diversify because herbivore

pressure temporarily reduced• Herbivores evolve resistance to toxic plant

compounds• Herbivores speciate onto formerly toxic

plants• Repeat first step- again and again

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Diversification ofAngiosperms

Herbivorous insectdiversification at same time

Parallel phylogenies undercoevolution

Good example of coevolution

• Bursera trees live insame area asBlepharida beetles

• Plants producespectacular toxin thatimmobilizes potentialherbivores

More on Bursera/Blepharida

• Flea beetlesspecialized onBursera

• Derived beetleshave specificmethods tocircumventplant defense

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Kinds of plant insectinteractions

• Plant herbivore interactions• Plant pollinator interactions• Insects protecting plants from

herbivory (domatia)• Insects as seed dispersers

Insects as pollinators• Plant evolves reward for insect visitor• Insect evolves behavior and/or structure to

enhance pollination• Benefits to plant

– More reliable pollination– Less pollen mixing

• Costs to plant– Dependence on insect– Cost of reward

• Cheating– Plant doesn’t offer reward (orchids)– Insect consumes seeds (yucca moth)

Types of insect pollinators• Beetles

– Oldest pollinators– Often attracted toflowers near ground,smell like fermentedfruit

• Flies– Some attracted tocarrion or dung smell

– Others feed on pollen

• Hymenoptera– Sweet nectar– Mouthparts match flower

• Butterflies and moths

Principal Insect Pollinators

Columbinecoevolution

• a. bees• b. long tongued

bees• c. bumblebees• d. hummingbirds

Hawkmoths