Temperature and development in host-parasite relationships

The effects of temperature on growth and development of the cabbage butterfly, Pieris rapae, and three wasp parasites: Apanteles rubecula, Apanteles glomeratus and Pteromalus puparum in Vancouver, Canada, and Canberra, Australia, are examined. We compare the estimates of temperature threshold for development and the number of degree-days above this threshold required to complete development for the immature stages of all species in both localities. Developmental patterns of both the host and its parasites differ between localities. Within the range of temperatures likely to be experienced during the host's breeding season, Australian parasites have longer generation times than their host at low temperatures and shorter generation times at high temperatures. Canadian parasites have shorter generation times, relative to the host, at all temperatures. This may be necessitated by the shorter breeding season available to the Canadian parasites.Besides temperature, parasite development is affected by host size and, in the gregarious species, parasite density. Host larval development is retarded by both Apanteles.All parasites are smaller at higher temperatures and males are smaller than females, but size is also affected by host size and parasite density.Although parasite size, and consequently fecundity, varies greatly, parasites experiencing similar temperatures will have closely similar developmental periods. The ecological significance of these developmental responses is discussed.