The role of chemical cues in host finding and acceptance by Callosobruchuschinensis

We studied the response of female Callosobruchus chinensis to chemical cues emitted by cowpea seeds at different stages of bruchid infestation (uninfe sted, egg carrying, L1-, and L4-infested). Olfactory attractiveness was det ermined in Y-tube olfactometer assays by testing individual seed categories against either clean air or uninfested seeds. Oviposition preferences betw een uninfested and infested seeds were determined in petri-dish choice-expe riments. The olfactometer assays revealed that weevils discriminate between seeds containing different stages of developing bruchids on the basis of o lfactory cues. While odors from uninfested and egg-carrying seeds acted as attractants, odors from L1- and L4-infested seeds failed to induce a positi ve response by the bruchids. When given a choice between uninfested and inf ested seeds in the olfactometer, weevils preferred uninfested seeds over L1 - and L4-infested seeds, but failed to distinguish between uninfested and e gg-carrying seeds. In the oviposition experiment as well, bruchids showed a distinct preference for uninfested seeds when offered in combination with L1- and L4-infested seeds. This experiment further showed a reduced accepta nce of egg carrying seeds. Our results indicate that C. chinensis females u se chemical information during both host searching and host acceptance. Vol atiles from uninfested or egg carrying seeds act as attractants, while dete rrence increases as development of bruchid immature stages progresses.