DEVELOPMENTAL SCHEDULES AND PERSISTENCE OF EXPERIMENTAL HOST-PARASITOID SYSTEMS AT 2 DIFFERENT TEMPERATURES

In experimental systems of a bruchid host, Callosobruchus chinensis, a nd a braconid parasitoid, Heterospilus prosopidis, the effects of chan ges in developmental schedules were examined in relation to the persis tence of the system, or the time to extinction of a component species. We modified the developmental schedules by changing the temperature f rom 30 degrees C to 32 degrees C. To compare persistence, a long-term system with overlapping generations was set up and the bruchid host re source, azuki beans (Vigna angularis), were renewed every 10 days. The long-term systems showed greater persistence at 30 degrees C than at 32 degrees C. Parasitoid extinction was often observed. We examined di fferences in life-history characteristics of the component species bet ween the two temperatures by short-term, single-generation experiments . Fecundity and egg hatchability of the host were reduced and the deve lopmental period of the parasitoid was shortened at 32 degrees C. The age at which the host became vulnerable to parasitoid attacks was earl ier at 32 degrees C than at 30 degrees C. We constructed a daily based , age-structured model to analyse which life-history change(s) affecte d the persistence of the long-term systems. The density-dependent popu lation growth of the host was described by a logistic equation and the attack rate of the parasitoid by a type II functional response with m utual interference. The simulation results showed greater persistence at 30 degrees C than at 32 degrees 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. Furt her, persistence at another temperature, 28 degrees C, was predicted u sing a model based on short-term data on the host.