Potentiation of Pest Control by Insect Immunosuppression

ABSTRACT: Potentiation of pest control by insect immunosuppression Lepidoptera is one of the most important insect orders agriculturally because of its detrimental, global impact on human nutrition and economies, defoliating crop plants, feeding on fibers, fruits and vegetables, and infesting stored foods. Biological control of these pests is important in reducing the need for non-specific insecticides hazardous to the environment and human health. Baculoviruses highly pathogenic to Lepidoptera and non-pathogenic to mammals have been developed and registered as biological pesticides. But, the restricted host range of many baculoviruses, limits their use to single or few closely related Lepidopteran species and is an obstacle to extending their implementation for pest control. Further development of novel baculovirus as well as other biological-control-based means for Lepidopteran pest control, demands a better knowledge of insect defense mechanisms. Lepidopteran immune responses to virus infections are poorly understood. The PIs have developed an original model system to study the Lepidopteran antiviral immune response based on Spodoptera littoralis resistance to AcMNPV (Autographa californica multiple nucleopolyhedrovirus) infection and the fascinating immunosuppressive activity ofCiV and CsV polydnaviruses (Chelonus inanitus and Campoletis sonorensis viruses, respectively). In this study our aim is to elucidate the mechanisms through which the immunosuppressive insect polydnaviruses promote replication of pathogenic baculoviruses in lepidopteran hosts that are mildly or non-permissive to virus- replication We will: 1- Assess the extent to which and the mechanisms whereby the immunosuppressive CiV and CsV polydnaviruses or their genes enhance replication of a well-characterized pathogenic baculovirus AcMNPV, in polydnavirus-immunosuppressed H zea and S. littoralis insects and S. littoralis cells, hosts that are mildly or non-permissive to AcMNPV. 2- Identify CiV and CsV genes involved in the above immunosuppression (e.g. inhibiting cellular encapsulation and disrupting humoral immunity). We have shown that S. littoralis larvae mount an immune response against AcMNPV that suppresses the viral infection, and demonstrated that CiV and CsV enhance AcMNPVs pathogenicity and infectivity to S. littoralis larvae and cells, respectively. This study will provide insight into molecular mechanisms of viral pathogenesis and anti-viral insect immunity. This knowledge is fundamental to develop novel means for pest control that strategically weaken insect defenses to improve pathogen infection and virulence and to control insect vectored diseases of humans, animals and plants. Our approach includes biochemistry, molecular biology, virology and bioassays on target pests.