Effect of sensitization on the orientation response of Cotesia plutellae females towards the odour of cruciferous host plant and host larval body extracts.

The importance of odour learning in host habitat and host selection is well demonstrated in many insects. In this present study using Cotesia plutellae Kurdjumov as a model, we examined the capacity of naive C. plutellae females to learn and orient towards the odour of cruciferous host plant, host larval body extracts of Plutella xylostella (L.), larvae reared on different host plants in a 'Y' tube olfactometer by repeated exposure. The acquired capability to recognize an odour by repeated exposures (sensitization) to a particular odour produced a strong decline in orientation time of wasps to the odour source. The decline in orientation time at 5 th exposure level was at least 55% and 36%, respectively, for virgin and gravid females to HPLE odours in relation to first exposure level. Whereas the HLBE odours elicited 49% and 51% decline in orientation time, respectively in virgin and gravid females compared to 1 st exposure level. Briefly, the gravid females oriented much faster toward larval body odours compared to host plant odours; while, virgin females were more attracted and rapidly oriented to host plant odours compared to larval body odours, signifying some synomonal/kairomonal substances are involved in influencing the orientation. The rapid orientation response observed for various infochemical extracts demonstrate that C. plutellae upon sensitization can respond to the chemical signals of most preferred odour in a host plant-herbivore complex associated with cruciferous crop ecosystem.