FUNCTIONAL-RESPONSE AS A COMPONENT OF DYNAMIC SIMULATION-MODELS IN BIOLOGICAL-CONTROL - THE CATOLACCUS-BOLL WEEVIL SYSTEM

A simulation model using Time Varying Distributed Delays was created o n the HERMES (Hierarchical Environment for Research Modelling of Ecolo gical Systems) of the USDA/ARS with the purpose of evaluating differen t forms of functional response components in dynamic simulations of bi ological control systems. The specific host-parasitoid life system use d in the evaluation was the boil weevil-Catolaccus grandis system. Fou r forms of functional response equations were tested: Type I, Type II, a Type II modified to yield constant attack probabilities under const ant host:parasitoid ratios, and a temperature-dependent Type II. Simul ation runs showed that the parasitoid is potentially capable of consid erable suppression of the host population. Predicted host numbers unde r Type I and II equations did not differ markedly, because realistic h ost numbers per parasitoid were often found in the linear portion of t he Type II equation. The probability of attack using a Type I equation was always near 100% despite arbitrarily increasing the host populati on to create a wide range of host:parasitoid ratios. The Type II equat ion resulted in fluctuating attack probabilities which steadily declin ed as host:parasitoid ratio exceeded 100:1. The modified Type II equat ion yielded attack probabilities starting at 52% and steadily declinin g to about 8% when host:parasitoid ratios neared 1000:1. We introduced a realistic, but hypothetical, relationship between functional respon se and temperature. Simulations using actual weather data from the Rio Grande Valley of Texas suggest that there is little difference betwee n using Types I or II equations, but that the effect of temperature on attack rates is substantial in this system. Caution should be used wh en incorporating data from experiments into simulation models because experimental conditions are often unrealistically optimal. We discuss the possible importance of temperature and other diurnal or environmen tal events on functional response and the value of relevant data in th is and other simulation models of biological control.