GROWTH-BASED APPROACH TO MODELING THE DEVELOPMENTAL RATE OF ARTHROPODS

The developmental rate of insects is an important parameter in studies of insect population dynamics as well as in biological and chemical c ontrol of agricultural pests. Traditionally, models used to predict de velopmental rates are empirical functions of temperature. Such models are limited from a theoretical perspective because they are not explan atory and fail to include the known effects of variables other than te mperature in determining developmental rate. A new approach is develop ed here that is based on the assumption that each species has a charac teristic size (mass) at the completion of its larval or nymphal stage and that the rate of growth to this ultimate size determines the rate of development. Growth rate is modeled as a function of consumption ra te and respiration (influenced by temperature) as well as approximate digestibility (influenced by diet quality). An analytic solution of th is growth rate model gives the developmental rate as a function of tem perature and diet quality. This approach was applied to a grasshopper, Melanoplus sanguinipes. Reasonable parameter choices generated a real istic developmental rate curve. Advantages of this approach over previ ous models include (1) the model is mechanistic and explanatory, (2) d evelopment is a function of nutrition as well as temperature, (3) the parameters have clear ecological meanings and are, for the most part, directly measurable, and (4) variable weight at the end of the life st age can be included in the model.