DIAPAUSE AND THE SEASONAL ECOLOGY OF THE INTRODUCED PARASITE, COTESIA (APANTELES) RUBECULA (HYMENOPTERA: BRACONIDAE)

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Abstract
The insect parasite Cotesia rubecula (Marshall) shows a long-day, photoperiodic response that results in diapause in the eonymph. Within the region of the critical photoperiod, the diapause response is modified by temperature and by the duration of the developmental period of the larval parasite, but in field populations in Vancouver, diapause is predominantly a response to short photoperiods. There is evidence that the parasite's response is largely independent of the host's response. Once diapause is induced, there is an obligatory dormant period of at least 2 months after which diapause terminates when specific-heat requirements are fulfilled. The estimated heat requirements are used to predict the date of diapause termination and the emergence of parasite adults in the field. Parasite activity begins almost 6 weeks after that of its host.The critical photoperiod for populations in Vancouver, Canada, lies between 15- and 16-h photophase but in Canberra, Australia, the critical photoperiod is less than 13 h. The significance of this difference in the diapause response of the 2 introduced populations is discussed and recommendations are made for further biocontrol efforts.
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