Interactions of temperature and dietary protein concentration in growth and feeding of Manduca sexta caterpillars

Temperature and the protein content of food affect rates of consumption and growth in herbivorous insects in different ways: reduced temperature typic ally reduces both consumption and growth rates, whereas reduced dietary pro tein typically increases consumption rate but either reduces or has no effe ct an growth rate. The: interactions between temperature and dietary protei n concentration in affecting consumption, growth and efficiency in fifth-in star caterpillars of Manduca sexta were studied, using both short-term (4h) and long-term (duration of fifth stadium) experiments. The short-term expe riments examined constant temperatures between 14 and 42 degrees C, whereas the long-term experiments examined constant temperatures between 18 and 34 degrees C; both experiments considered two levels of dietary protein. In b oth expects, caterpillars had significantly higher consumption and Erase pr oduction rates on low-protein compared with high-protein diets at each test temperature between 18 and 34 degrees C, thereby compensating for the lowe r diet quality. In contrast, at more extreme temperatures (14 and 42 degree s C) in the short-term studies, consumption and frass production rates were lower on low-protein compared with high-protein diets. As a result, there were substantial interactions between temperature and dietary protein for c onsumption and frass production rates in the short-term experiments, but no t in the long-term experiments. These results suggest that interactions bet ween temperature and dietary protein may emerge because of.,the failure of compensatory feeding responses at low and high temperatures. It is hypothes ized that the failure of compensatory responses is more Likely to occur und er diurnally fluctuating temperatures than under a constant temperature wit h the same mean, and it is proposed that interactions between temperature a nd dietary protein for consumption are relevant to M. sexta and other cater pillars that experience wide diurnal fluctuations in temperature in the hel d.