| Interspecific competition between parasitoids not only have effects on the size,structure and stability of insect population,but also on biological control using parasitoids.Meteorus pulchricornis and Microplitis mediator,important parasitoids of lepidopteran pests,are potential competitors because they overlap to some extent from each other in the geographical distribution and host range.We investigate intrinsic competition between the two parasitoids to provide data for evaluating their control effects in biological control practices.This thesis study addresses three questions:(1)Which parasitoid have competitive superiority in the intrinsic competition?(2)Which factors affect their competition?(3)What are effects of intrinsic competition to developmental performances of offspring parasitoids in two parasitoids?Main results and conclusions obtained from the study are summarized below.1.Intrinsic competition between M.mediator and M.pulchricornis as affected by host larval instars,parasitizing sequence and time intervalsWe examined intrinsic competition between M.mediator and M.pulchricornis in the shared host Mythimna separate,as affected by host larval instars,parasitizing sequence and time intervals between two parasitism.The results showed that host larval instars had no significant influence on the competition outcome,but parasitizing sequence and time intervals did.Under all treatments with parasitizing sequence and time interval,the developmental survival of M.mediator were lower than that of M.pulchricornis,except for being in 8-day-old host larvae that were previously parasitized by M.mediator 24 h ahead,where M.mediator survival rate(56.50%)was higher.The developmental survival of M.mediator are higher than that of M.pulchricornis,In 4-day-old host larvae that were previously parasitized by M.pulchricornis 24 h ahead,where M.mediator survival rate(3.30%)is the lowest The results of this study suggest that M.pulchricornis has competitive superiority over M.mediator in interspecific competition in parasitizing M.separate larval hosts.2.Developmental performances of offspring parasitoids under the intrinsic competition between M.mediator and M.pulchricornisTo examine the effects of intrinsic competition between M.mediator and M.pulchricornis on developmental parameters of progeny parasitoids.We observed developmental period,body size and adult longevity of offspring parasitoids survived through the competition as affected by host larval instars,parasitizing sequence and time intervals.Compared with non-competition,interspecific competition significantly prolonged M.pulchricornis larval development period and adult longevity while decreased adult body size.Interspecific competition significantly shortened M.mediator progeny development period and adult longevity in 4-day-old hosts,but prolonged the progeny development period and decreased adult longevity in 8-day-old hosts.No significant differences were found between interspecific competition and non-competition in offspring adult body size of M.mediator.The results suggest that intrinsic competition between M.mediator and M.pulchricornis exerts more negative impact on M.pulchricornis than on M.mediator.3.Comparison in host discrimination ability between M.mediator and M.pulchricornisTo evaluate the recognition ability of competing wasps in parasitism selection,we exposed a healthy and a parasitized host to a parasitoid for parasitizing selection,with the parasitized host by either species of parasitoids and the wasp with or without the parasitizing experience.The results showed that both M.pulchricornis and M.mediator were able to discriminate in favor of unparasitized hosts.Cumulative hazards of hosts being parasitized by experienced M.mediator and M.pulchricornis significant higher than that by non-experienced M.mediator.and M.pulchricornis.The results suggest that parasitizing experience significant differences in host discrimination and M.pulchricornis requires more time to discriminate hosts than M.mediator. |
