| Global warming causes an increase in the average temperature,intensity and frequency of extreme climatic conditions,such as short heat waves,in the past 20 years.Extreme temperatures can impact parasitoid growth and development in its hosts.Meteorus pulchricornis is an important parasitoid natural enemies of numerous lepidopteran defoliator pests.Parasitism biology and ecology of M.pulchricornis have been studied in recent years.However,little is known about effects of heat stress(such as short heat waves)on developmental parameters and functional responses of this parasitoid.This thesis study was to investigate occasional and persistent heat stress on developmental parameters of M.pulchricornis at larval and pupa stages on developmental parameters of M.pulchricornis and its functional responses.The main results and conclusions are summarized as follow.1.Effects of occasional heat stress on developmental parameters of M.pulchricornisTo examine the effect of occasional heat stress on parasitic natural enemies of insect pests,we made laboratory experiments to examine developmental performances of the offspring of the solitary endoparasitoid,M.pulchricornis,using S.litura larvae as hosts.Offspring parasitoids in the hosts received the heat treatment by 39℃ for 4 hours at the age of 1,2,3,4,5,or 6 days old after parasitism.We observed developmental survival,duration,adult body size,and longevity of offspring parasitoids.Larval survival to pupa decreased in the host larvae when receiving the heat treatment at the age of 1 and 5 d,by 36.1%and 28.6%,respectively,compared to the control.Larval duration was prolonged by 5.0%,5.2%,7.0%,and 12.1%,respectively,in the host larvae when receiving the heat treatment at the age of 2,3,5,and 6 d,respectively,compared to the control.Adult hind tibia length decreased by 1.8%and 2.6%,respectively,in the hosts when receiving the heat treatment at the age of 5 and 6 d.Pupa-to-adult duration,pupa-to-adult emergence rate,and adult longevity were not influenced by the heat shock treatment.The results of the present study suggest that older larvae of M.pulchricornis were more vulnerable to heat waves than younger ones.The pupa of M.pulchricornis received the heat treatment at the age of 1,3,or 5 days old.Compared to the control,pupa-to-adult duration was prolonged by 7.7%and 16.3%,respectively,when pupa receiving the heat treatment at the age of 1 and 5 d.Adult longevity was decreased by 25%when pupa receiving the heat treatment at the age of 5d,compared to the control.Pupa survival to adult and adult hind tibia were not influenced by the occasional heat treatment.The results of this study suggest that M.pulchricornis older pupae were more vulnerable to heat waves than younger ones.2.Effects of persistent heat stress on developmental parameters of M.pulchricornisTo examine effects of persistent heat stress on development parameters of M.pulchricornis,offspring parasitoids in the hosts received the heat stress treatment at varying levels in time for1,2,3,4,5 or 6 days at the age of 1-day old after parasitism.Larval survival to pupa and adult hind tibia length decreased with increasing duration of heat stress,with a linear relationship between larval duration and heat stress duration.The similar pattern to larval duration applied to pupa-to-adult duration.Adult longevity was not influenced by the heat shock treatment.The results of the study suggest that strong persistent heat waves have negative effects on development parameters of M.pulchricornis.3.Effects of heat stress on functional responses of M.pulchricornisWe investigated parasitizing responses of M.pulchricornis individuals to S.litura larvae at varying densities from 1,5,10,15,20 to 30 per box during 12 h,in which heat stress treatment was imposed for 6 middle hours.Sugar food was supplied to the parasitoid that was 5-or 6-days old without parasitic experience.Results were in line with the prediction of the Holling-Ⅱ response model.The number of parasitized larvae increased with initial increase of larva density,and then leveled off when larval host density further increased.Compared to the control,searching efficiency decreased under heat stress.The attack rate decreased while handling time increased under the heat treatment,compared to the control.Our results suggest that heat stress may decrease the functional responses of M.pulchricornis to host larvae. |
