Plant-herbivore interactions

2. Plant-herbivore interactions “an inordinate fondness for beetles” -Haldane

3. Interactions can be classified by the effect they have on the species involved

4. General types of interactions and their outcomes Type Consequence partner 1 partner 2 competition - - parasitism / predation* - + mutualism* + + commensalism?0 + amensalism?0 - * Directly relevant to plant-insect interactions ? May occur in plant-insect interactions

5. Lifestyles of herbivores: Monophagous, single food type SPECIALIST  Oligophagous, few food types SPECIALIST Polyphagous, many food types GENERALIST

6. What Do Plants Provide? • Fats - low except seeds and some fruits • Proteins - < 2% of biomass – Amino acid balance different than animals’ • Carbohydrates - mostly indigestible – cellulose, hemicellulose, in cell wall • Vitamins and Minerals • Defensive Chemicals and Structures • All nutrients generally at much lower tissue concentrations in plants than in their consumers

7. Generalists Specialists Pros • - Predictable defenses • Easier decision-making • Finding mates? - Many food options - Flexibility to avoid predators Cons - Finding the right food - Specific plant defenses - Avoiding predators - Competition for food? - Variable host quality - Host-finding decisions - Finding mates? 90% of insect herbivores are specialized 1% of mammal herbivores are specialized

8. How do herbivores choose their food? Generalists Nutrient constraints Detoxification limitations Specialists Endosymbionts Detoxification enzymes There are many ways to exploit a plant…..

9. Types of plant feeding Leaf herbivory: most commonly studied Root herbivory Nectar robbing Florivory

10. Types of plant feeding Seed predation Galls, stem borers

11. Types of plant defenses to herbivory Constituative- defenses that are always present regardless of the presence of herbivory Induced- defenses that are only produced when there is feeding by an herbivore Physical- trichomes, spines, thornes Chemical- plant compounds derived from primary metabolism Tolerance - some plants may be adapted to withstand some degree of attack without fitness loss

12. Really cool plant defense examples latex

13. Really cool plant defense examples Bersera squirts toxic resin when fed upon -- terpenes under pressure Blepharida has evolved a behavior to overcome this defense Squirt up to 2 meters! Beetle trenches- takes 1hour to poke tiny holes in the mid-veins to release toxic resin After draining- the beetle takes 15 minutes to consume the leaf

14. Really cool plant defense examples Indirect defenses are plant traits that attract predators and parasitoids of herbivores which facilitate top-down control. Examples: constituative Ant-acacia Mutualism (+/+) induced Jasmonic acid and methyl jasmonate (MeJA) induce volitiles to attract natural enemies of the plant Beet armyworm-pest of cotton Parasitoid of armyworm

15. Really cool plant defense examples Plant communication?? Rick Karban – University of California, Davis Levels of defense chemicals in tobacco near damaged or undamaged sage brush Proportion tobacco plants damaged near clipped and unclipped sagebrush Proportion tobacco plants damaged near clipped and unclipped sagebrush

16. Herbivore offense: behavioral Feeding choices - Larval: Diet selection- chemoreceptors Supplemental food Diet mixing - Adult: oviposition Trenching

17. Herbivore offense: Physiological traits Enzymes: reduce effects of plant compounds salivary enzymes - inhibit induced plant defenses metabolic enzymes - e.g., metabolize nonprotein amino acids Sequestration: incorporate plant defenses into herbivores’ tissues to gain protection from predators/parasites Symbionts: allow digestion of cellulose, produce missing nutrients vector diseases to weaken plant defense

18. How well do plant defenses work and are herbivores successful at overcoming plant defenses?

19. Evaluation of the effect of induced chemical defenses on plants Wild radish (Raphanus sativus), insect herbivores, and induced defenses by Anurag A. Agrawal Experimental design 3 treatments: control = no defense clipped = simulated herbivory induced= defended by chemicals flea beetle aphids noctuid moth

20. Results: Increased levels of mustard oil glycosides in induced plants Significantly higher leaf damage on control plants Female fitness in induced plants was over 60% higher than controls treatment sampling date

21. Costs to plant to maintain defenses Frequency of leaf response (squirting)

22. Insects and plants affect each other’s fitness Parsnip webworm and wild parsnip May Berenbaum

23. Parsnip webworm and wild parsnip Parsnip established in NA in 1609 by European colonists Webworm invaded in 1869 In Europe (native range for both species) two furanocoumarins, sphondin and bergapten defend parsnip from herbivory Once in NA without insect, parsnip evolved lower levels of furanocoumarins (herbarium specimens studied) After introduction of webworms to NA, furanocoumarin levels increased # of plants examined

24. Evolution in furanocoumarin levels possible: Furanocoumarins produced by plant haveheritable variation Plants with higher furanocoumarin levels produce more offspring Evolution in insects possible: Furanocoumarin detoxification enzymes in insects have heritable variation Insects with higher levels of enzymes produce more offspring

25. Plant defenses as selective agents Defenses include: mechanical traits (thorns, spines, latex) digestibility reducers toxins recruitment of predators/parasitoids Conditions for defenses to exert selection on herbivore traits: (when you might expect evolutionary changes in the herbivore in direct response to the plant) • Defenses reduce herbivore fitness • Herbivores have genetically based traits to overcome defenses that improve herbivore fitness • -These traits are heritable and show variation

26. How do plant defenses reduce herbivore fitness? • Direct effects: • - Death from mechanical defense, toxins • Slow growth, reduced fecundity from digestibility reducers • Starvation/dehydration from deterrence due to toxins • Indirect effects: • Increased ‘window of opportunity’ for parasitoids • Greater detectability by predators or parasitoids Outcome: decrease in herbivore fecundity or number of offspring they produce

27. Possible outcome of the reciprocal selection pressure exerted on plants and herbivores

28. Coevolutionary arms race • Attack --> Defense --> Counterattack • Strong selection on plants to not be eaten because • herbivory reduces plant fitness • -Drives selection on herbivore ability to overcome defense because plant defenses reduce herbivore fitness • Initiates new round of plant defense • May lead to diversity of plant defenses and specialization between plants and their herbivores Consequences: Increased diversity of plants and herbivores

29. Hessian fly, Mayetiola destructor The most destructive pest of wheat worldwide Control: 27 resistance genes have been developed for wheat Different populations of flies have evolved to overcome these defenses Deployment of new resistance genes in a population of wheat are only effective against the fly for 8-10 years Sometimes a single amino acid change enables resistance in the fly

30. Adaptive radiation of beetles on flowering plants http://evolution.berkeley.edu/evosite/evo101/VIIB1bBeetles.shtml Brian Farrell (1998) -once beetle lineages switched to angiosperms, some of them diversified into lineages that specialize, feeding on different parts of the plant (root, seed, leaf, etc.) Beetles

31. Coevolution of mutualism (+/+) Star orchid Hawkmoth Long spur forces moths to pollinate flower Moths evolve longer probocis to feed effectively/ efficiently Plant evolves longer spur

32. Interested in plant-insect interaction courses/ research? Lynn Adler lsadler@ent.umass.edu http://www.people.umass.edu/lsadler ENTOMOL 597A: Insect-Plant Interactions