MODELING THE TEMPERATURE EFFECT ON BIMODALLY DISTRIBUTED LIFE TIMES

Data on the temperature and humidity relationships of Tetranychus dese rtorum Banks were reinvestigated to develop a model that describes the dependency between the time course of the adults' age-specific surviv al rates, on the one hand, and the temperature, on the other. The expe rimental data ascertained by Nickel (1960, Hilgardia, 30(2): 41-100) d iffer from other results, because they exhibit marked bimodally distri buted life times at the extremes of temperature. The bimodality vanish es at mild temperatures. The observed bimodality results from the fact that the population used in the experiments is divided into two subpo pulations with different relationships to the environmental conditions . The environment-dependent division of individuals into subpopulation s is important for at least three aspects. The first aspect concerns t he management of insect populations, the second one concerns the model development and the third one the design of the experiments. If the i ndividuals split into subpopulations, a different population dynamic w ill result, which will influence the choice of appropriate managment m ethods. With respect to the model development, mixed life time distrib ution functions are to be used to simulate the observed bimodality. Th e parameter estimation of these models requires a sufficient amount of data.