Effects Of Landscape Structures On The Fitness And Control Potentiality Of ParasitoidsCommunities Against On Asian Corn Borer,Ostrinia Furnacalis Guenée (Lepidoptera:Crambidae)

In recent years,the landscape structures have been dramatic changed because of the increasing human activities and the climate changes.Non-crops habitats in the field have gradually decreased,and the planting pattern has changed.Due to ongoing the changes of landscape structures in agricultural ecosystems,natural habitats are gradually decreased.These changes have an important impact on insects.Asian corn borer(Ostrinia furnacalis Guenée)is one of the major pests in corn fields,which seriously affects the yield and quality.In present,parastoids are an important biological agent against Aisa corn borer in China.The changes of landscape structure will have a potential impact on the parastoids.In order to determine the influence of landscape structure on the parastoids in the filed,our study explored the effects of landscape structure on the communities of larvae parasitiods,the effects of egg parasitiods and the control potentiality of parasitiods.The main results are listed as follows:(1)Macrocentrus.cingulum,Lydella.Grisescens,and Beauveria spp.are the major parasitoid species emerged from overwinter larvae.The populations of three parasitpoid species were significant influenced by the agricultural landscape structure,and the influence was varied in different spatial scales.In 250 m scale,the population of M.cingulum increased with the proportion of non-crop habitats(e.g.,grass,roads,and waters),and the population of L.grisescens increased with the proportion of grassland and cover field(p<0.01),while the infect proportion of Beauveria spp.was decreased with the Simpson's index of landscapes,grassland,roads,and water habitats(p<0.01).In 500 m scale,the population of M.cingulum was significant influenced by the Simpson's index(p<0.01).Besides,the effects on the populations of L.grisescens and Beauveria spp.were similar in both spatial scales.(2)None of the male ratio and the hind leg tibia length of Asian corn borer,brood size,male ratio and hind leg tibia length of M.cingulum,or pupal weigh and hind leg tibia length L.grisescens were significantly affected by the agricultural landscape structure.It shows that the influence of landscape structure on the community of parasitiods is mainly at the population level,but not at the individual level.(3)The scale effects of landscape structure on the parasitic rate of M.cingulum and L.grisescens were significant.The parasitic rate of M.cingulum and L.grisescens were not influenced by landscape structure in the scale of 250 m(p<0.01).However,the parasitism proportion of Asia corn borer was increased with Simpson's index and the proportions of noncrop and urban areas in 500 m scale(p<0.01).(4)In this study,Trichogramma.dendrolimi and Trichogramma.ostriniae are the major Trichogramma species in the corn fields.The parasitic rate and biological characteristics of Trichogramma varied among different agricultural landscape structures in both spatial scales.In 250 m scale,the spatial of egg masses significantly increased with the proportion of towns,road,and waters(p<0.01),while it decreased with the proportion of fields(p<0.01).However,in 500 m scale,the spatial of egg masses decreased with proportion of forest habitat area(p<0.01).(5)The Wolbachia infection frequency was significant increased by the proportion of forest,grassland,urban,and field habitats in both scales(p<0.01).The results showed that the agricultural landscape structure played an important role in affecting the species,quantity,the fitness and control potentiality of parasitoids in corn field conditions.The results provide the powerful references for making scientific measurements against agricultural pests by the structural improvement of agricultural landscape.