PARENT SESSION
Oral Session # 65: Herbivory V: Deer, Geese, and Chemistry.
Presiding: K Bjorndal
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.
Body size and N:P stoichiometry of insect herbivores vary with host plant chemistry.
Kay, Adam*,1, John, Schade2, Novotny, Amy2, Hernandez, Daniel1, Ogdahl, Megan1, Sterner, Robert1, Hobbie, Sarah1, 1 Department of Ecology, Evolution and Behavior, St. Paul, MN, USA2 Department of Zoology, Tempe, AZ, USA
ABSTRACT- Recent evidence suggests that fast-growing animals contain an abundance of P-rich ribosomal RNA and characteristically low ratios of N:P. If biochemical allocation depends on the relative availability of substrates, then the elemental contents and growth rates of consumers may vary with the C:N:P stoichiometry of their food. In this study, we investigated the relationship between the stoichiometries of two herbivores (the lace bug, Corythucha arcuata, and an unidentified aphid species) and the leaf N and P contents of their host plant (Quercus macrocarpa). To obtain leaves of variable quality, we sampled plots across a fire frequency gradient at different points in the growing season (June and August). We found correlated shifts in oak leaf and lace bug chemistry over the summer, as both leaf P:C and the P content of adult lace bugs were significantly higher in June than they were in August. In August samples, the size of adult lace bugs (measured as dry mass) was positively correlated with leaf C:N and C:P ratios, and negatively correlated with leaf N:P. These results suggest that lace bugs reached larger adult size by growing faster on leaves that are relatively rich in P. However, because lace bug P content decreased with body size, there was no relationship between lace bug %P and leaf C:P or C:N ratios. Unlike lace bugs, same-sized aphids contained significantly more P in August than they did in June, despite the lower C:P ratio in August oak leaves. In addition, aphid %P in August was negatively correlated with leaf N:P, and was significantly lower in control plots than it was in periodically burned plots. Our study provides the first demonstration in a forest ecosystem of herbivore C:N:P stoichiometry adjusting to host plant quality.
Key words: insect , fire, stoichiometry, herbivory