Behavioral processes and egg-laying decisions of the bean weevil, Callosobruchus maculatus

Empirical studies of behavioral processes were designed in a seed beetle, Callosobruchus maculatus, to distinguish between two alternative tactical models, namely, comparison tactics and threshold tactics of seed choice, and also to deduce the behavioral rule of its oviposition decisions. Search sequences and the oviposition process of the female bruchid beetle were observed and recorded. Analyzing data of the search sequence showed that the female bruchid beetle repeatedly encountered seeds randomly and tended to oviposit on a newly encountered seed in an ovposition bout. These results contradict the usual comparison models, which predict that the female will return to choose any one of the previously encountered seeds after sampling. In addition, the oviposition decision (rejection or acceptance of an encountered seed to oviposit) was analyzed with a generalized linear modeling (GLIM) technique. Modeling showed that the probability of accepting a seed with different numbers of eggs on it changed during her egg-laying process. This evidence supports the idea that the female is using a threshold tactic and that her acceptance threshold is being adjusted by experience gained during the egg-laying process. The analysis of statistical modeling also showed that both the time since the last oviposition and the number of eggs which had been laid by the female had a significant effect on the probability of accepting seeds with different numbers of eggs. Therefore, a time measuring system and the physiological state variable, e.g., eggload of the female, should be included in the behavioral rule to explore how the female makes her decision in the egg-laying process and to examine the importance of choice behavior as a component of selection and adaptation. Received: May 8, 1998 / Accepted: September 20, 1999