CUES FOR OVIPOSITION BY LADYBIRD BEETLES (COCCINELLIDAE) - RESPONSE TO APHIDS

(1) Reproductive responses of predatory insects to spatial variation in prey density are poorly understood, yet may contribute significantly to stability of the predator-prey interaction. To explore the nature of such responses for ladybird beetles in particular, the sensitivity of ovipositing females of Coccinella septempunctata L. to local prey conditions was examined in the laboratory. (2) Previously well-fed coccinellids laid significantly fewer eggs when removed temporarily from aphids than when kept with aphids. The drop in egg production resulted from beetles delaying oviposition for several hours when aphids were absent. (3) The coccinellids did not delay oviposition when exposed to aphid odours and honeydew (but not to aphids). (4) Female beetles were more active when aphids were absent than when they were present. Females were also more active when only aphid odours and honeydew were present than when aphids were present. Thus, the females'' delay in ovipositing in the absence of prey did not result simply from their increased activity. (5) The reluctance of coccinellids to oviposit, coupled with these females'' increased activity when aphids are not nearby, enhances the ability of these predators to oviposit at particularly favourable sites.