Oviposition in Cryptolaemus montrouzieri stimulated by wax filaments of its prey

The oviposition responses of Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) to the soft scale Eupulvinaria hydrangeae (Steinweden) (Homoptera: Coccidae) and to the mealybug Planococcus citri (Risso) (Homoptera: Pseudococcidae) have been compared in the laboratory. The females delay oviposition and withhold mature eggs in their lateral oviducts in the absence of wax filaments produced by the prey (only present in the ovisac of E. hydrangeae, present in all stages of P. citri). Contact chemical cues perceived by females when probing the wax filaments with their mouthparts are the signals inducing the search for oviposition sites. The second step is under the control of the ovipositor by which females locate confined sites to lay eggs. This oviposition behaviour could have a considerable impact on the prey exploitation strategy of this important biocontrol agent and might help to understand its apparent ineffectiveness in situations of low prey density.