UBC Theses and Dissertations
Development, diapause and seasonal ecology of the insect parasite, apanteles rubecula (hymenoptera; braconidae) Nealis, Vincent Graham
Apanteles rubecula is a solitary insect parasite of Pier is rapae (small cabbage white butterfly, imported cabbageworm). The parasite has been successfully introduced to Australia and Vancouver, Canada but has failed to become established at other North American release sites. This practical problem illustrates a fundamental aspect of insect ecology. The seasonal biology of insects is interpreted here as an interaction of responses to ambient conditions. Emphasis centers on the rates at which life history phenomena occur and the importance of the insect's biological chronometers on the outcome of its ecological relationships with its host and its local climate. Comparisons are made between Canberra, Australia and Vancouver, Canada. The parasite's developmental response to temperature is similar in Canberra and Vancouver but the host response differs. Canberra A. rubecula have a longer generation time relative to the host at low temperatures, but shorter generation times at higher, midseason temperatures. Vancouver parasites always have faster generation times than their hosts but the season is truncated in August by a diapause response to daylengths shorter than I5h. The beginning of the season is delayed until late May by the high thermal requirement to terminate diapause. These local responses to temperature and photoperiod result in different phenologies which, while appropriate locally, are disastrous elsewhere. The failure of North American attempts to establish Vancouver A. rubecula is attributed to the diapause characteristics of the released insects. They entered diapause while ambient temperatures remained warm enough for morphogenesis and were unable to survive the obligatory period to diapause termination. Manipulation of the diapause response is one technique in ecological pest management. A methodology for a breeding program and its analysis is presented. Practical suggestion for biological control efforts are made and the role of individual physiological responses in insect seasonal ecology are discussed.