A Preliminary Study On Nutrition Ecology Of Harmonia Axyridis(Coleoptera:coccinellidae)

Harmonia axyridis is an important predatory natural enemy in China,playing a vital role in controlling aphids.So far,there have been many studies on its oviposition behavior,but less attention focuses on the oviposition of trophic eggs.Trophic egg oviposition,an adaptive maternal strategy,has important influence on survival and development of hatched larvae.In this thesis study,trophic egg oviposition was investigated in the field for the fac-tors including aphid abundances,the existence of other ladybird eggs,and others.and La-boratory experiments were made to examine factors for oviposition of trophic eggs.In ad-dition,the effect of starvation on the fourth-instar larval development was also examined.The main results and conclusions obtained from this study are as follows.1.Observation study of factors for trophic egg oviposition by H.axyridisH.axyridis egg clusters were collected from different habitats in the field and brought to laboratory to hatch.The analysis results showed that the proportion of trophic eggs in an egg duster was affected by oviposition plant species,aphid species around,egg cluster size,and the presence of other ladybirds,but not by aphid density,the presence of other lady-bird's egg clusters,and the distance of oviposition site from aphids.The proportion of trophic eggs on Vicia sepium was significantly higher than that on both V.faba and Lager-stroemia indica,and greater with the presence of ladybirds than without.The presence of aphids Aphis craccivora,Megoura japonica,and Tinocallis kahawaluokalani influence the trophic eggs in proportion significantly.The results of this study suggest that H.axyridis makes decisions on laying trophic eggs in response to plant species aphid species,egg cluster size,and the presence of other ladybird beetles.2.Effects of prey abundances and the presence of other ladybird eggs on the trophic egg oviposition of H.axyridisBy manipulating different levels in aphid abundances(30/d,60/d,90/d,constant 30/d,and constant 60/d),the proportion of trophic eggs was observed.The proportion under the constant levels in aphid abundances was significantly lower than that under the non-constant counterparts,and with increasing aphid abundances,but did not change with egg cluster size.The proportion of trophic eggs was examined in the presence of conspe-cific,Propylaea japonica egg clusters,or both.The results showed that the trophic egg proportion was significantly higher in the presence of both ladybirds' eggs than of anyone ladybird's eggs,and in the presence of P.japonica egg clusters than of conspecific egg clusters.H.axyridis preyed more P.japonica eggs than conspecific eggs in the presence of either of them,but did not show preference in the presence of both of them.The results of this study suggest that prey aphid abundances the presence of ladybird's egg clusters influ-ence the trophic egg proportion at oviposition in H.axyridis.3.Effects of starvation stress on H.axyridis larval developmentLadybird beetles often face temporary food shortage during their life.To examine ef-fects of food shortage on H.axyridis in developmental performances,we conducted labor-atory experiments,using the 4th instar larva as the testing insect,one of the most starva-tion-resistant stages,and the bird cherry-oat aphid Rhopalosiphum padi as the food prey.We examined larval development time,survival,adult body size and longevity as affected by starvation treatment and initial larval body weight.H.axyridis larva did not survive to pupa under "no feeding" and "feeding for 1 day" treatments.Pupation probability increased from 46%with a increase in initial body weight under the "feeding for 2 days" treatment,but was 100%without relation to the initial body weight under respective treatments of feeding for 3 and 4 days.Larval development time to pupa was influenced by both starva-tion treatments and initial larva body weight,decreasing by 58%and 30%under "feeding for 3 days" and "feeding for 4 days" as compared to "feeding for 2 days" The development time showed slight increase with initial body weight under the treatments of feeding for 2 and 3 days.Adult body weight was influenced by starvation treatments,but not by initial larva body weight,increasing respectively by 63.7%and 72.5%under treatments of feeding for 3 and 4 days as compared to feeding for 2 days.Adult longevity was not influenced by initial larva body weight,increasing by 27.5%with "feeding for 4 days" as compared to"feeding for 2 days".The results of this study suggest that H.axyridis 4th instar larva upon molting requires more than two days feeding on aphids to accomplish the development to adulthood.