Developmental Interaction Performances Between Mythimna Seperata And The Parasitoid Meteorus Pulchricornis Under Wheat Drought Stress

As an important abiotic factor,water has critical effects on growth and development of crop plants,with accompaniment influence on the pests of the crops and the natural enemies parasitizing the pests.The extreme weather due to climate change is generally expected in the future,which may cause more frequent drought.While prime focus has been put on effects of drought on crops,less attention has been given to the influence of crop drought stress on interactions between insect pests and their parasitic natural enemies linked with the crops.To provide more data to understand those interactions and therefore to enhance conservation of natural enemies in biological practices,this thesis study was to investigate drought effects in wheat plants on herbivorous Mythimna seperata caterpillars in food use efficiency and life history and on the parasitoid of Meterous pulchricornis in developmental performances.The main results and conclusions are summarized as follow.1.Effects of wheat drought on M.seperata in developmental performancesDrought treatments were imposed on potted wheat seedlings at varying levels from 0.00 g·mL-1(control),0.05 g·mL-1(low),0.10 g·mL-1(medium)to 0.20 g · mL-1(high)of Polyethylene Glycol(PEG)6000 in water.Development time,survival and body size of M.seperata were examined.Results showed that the drought stress treatment decreased pupal weight,pupa duration,adult body weight and survival rate,while prolonging duration of larvae and increasing adult eclosion rate.Compared to the control,the heavy drought treatment extended larval development time by 4.6%,decreased pupa time by 3.3%,reduced pupa weight by 11.76%,and decreased adult body weight by 33.33%.The heavy drought treatment also reduced larval survival by 21%,but increased adult eclosion rate by 18%.The results of this study suggest that heavy drought to wheat plants can have negative effects on M.seperata in developmental performances.2.Effects of wheat drought on M.seperata in food utilizationWe imposed drought treatments on potted wheat seedlings at varying levels from 0.00 g·mL-1(control),0.05 g · mL-1(low),0.10 g·mL-1(medium)and 0.20 g·mL-1(high)of Polyethylene Glycol(PEG)6000 in water.We measured food consumption and utilization efficiency of M.seperata larvae,and used ANCOVA and classical indices to evaluate effects of plant drought.The ANCOVA results showed that drought stress treatment decreased food consumption and body weight gain of larvae,decreasing by 10.4%in food consumption and 10.6%in body weight gain at the high drought level,compared with the control.But the drought did not affect M.seperata larvae in food digested.Analyses of classical food utilization indices showed that the high level of drought stress reduced the efficiency of conversion of digested food by 8.0%,but increased the approximate digestibility by 10.5%,compared with the control.Results of this study suggest that moderate and heavy drought to wheat plants can decrease food utilization efficiency of M.seperata larvae.3.Effects of wheat drought on M.pulchricornis in developmental performancesWe imposed drought treatments on potted wheat seedlings at varying levels from 0.00 g·mL-1(control),0.05 g·mL-1(low)and 0.20 g·mL-1(high)of Polyethylene Glycol(PEG)6000 in water.Results indicated that drought stress did not affect parasitism rate,adult eclosion rate,pupal duration and adult life-span of offspring,but significantly influenced egg-to-pupation time,pupal weight and offspring parasitoid body size.The medium drought treatment extended egg-to-pupation time to 243.07 h,as compared to thecontrol(229.15 h),while the heavy drought treatment had no significant effect.But the heavy drought treatment decreased offspring parasitoid pupal weight by 3.8%and hind tibia length to 1.57 mm,as compared to the control.The results suggested that drought stress can have negative influence on developmental performances of M.pulchricornis.