Developmental schedules and persistence of experimental host-parasitoid systems at two different temperatures.

In experimental systems of a bruchid host, Callosobruchus chinensis, and a braconid parasitoid, Heterospilus prosopidis, the effects of changes in developmental schedules were examined in relation to the persistence of the system, or the time to extinction of a component species. We modified the developmental schedules by changing the temperature from 30°C to 32°C. To compare persistence, a long-term system with overlapping generations was set up and the bruchid host resource, azuki beans (Vigna angularis), were renewed every 10 days. The long-term systems showed greater persistence at 30°C than at 32°C. Parasitoid extinction was often observed. We examined differences in life-history characteristics of the component species between the two temperatures by short-term, single-generation experiments. Fecundity and egg hatchability of the host were reduced and the developmental period of the parasitoid was shortened at 32°C. The age at which the host became vulnerable to parasitoid attacks was earlier at 32°C than at 30°C. We constructed a daily based, age-structured model to analyse which life-history change(s) affected the persistence of the long-term systems. The density-dependent population growth of the host was described by a logistic equation and the attack rate of the parasitoid by a type II functional response with mutual interference. The simulation results showed greater persistence at 30°C than at 32°C. Sensitivity analysis showed that there are threshold boundaries in the length of the vulnerable period of the host beyond which system persistence drastically changes. Further, persistence at another temperature, 28°C, was predicted using a model based on short-term data on the host.