Gypsy moth larvae show increasing resistance toward its baculovirus Lymantria dispar M Nucleopolyhedrovirus(LdMNPV) as they age within the instar, a phenomenon referred to as developmental resistance. We found that developmental resistance in gypsy moth has a systemic basis because gypsy moth larvae show increasing resistance to fatal infection when the virus is delivered not just orally, but intrahemocoelically as well. Although developmental resistance to mortality by baculovirus as larvae age within the instar is not a unique phenomenon, what is unique in this system is that the basis for this resistance is in large part systemic, i.e., not mediated by the midgut as reported in other host-baculovirus systems. Having ruled out the possibility that developmental resistance of gypsy moth larvae is related to increasing larval weight at the time of inoculation, we hypothesized that systemic developmental resistance may involve a hormonally mediated immune response. To test this hypothesis, we injected an immunosuppressive agent, diethyldithio-carbamic acid (DDCA), with budded virus of LdMNPV into the hemocoel of developmentally-staged gypsy moth larvae. Injection of DDCA eliminated developmental resistance. To further explore this hypothesis, we are measuring the impact of DDCA on the activity of two critical marker enzymes of insect cellular immunity, FAD-glucose dehygenase (GLD) and phenoloxidase (PO). In addition, we are investigating whether GLD and/or PO activities increase after inoculation with LdMNPV and if this activity is consistent with the onset of developmental resistance. We further plan to explore the possible role of juvenile hormone and ecdysone in this form of resistance. These results may provide the first direct evidence of systemic developmental resistance due to an immune response to viral infection in insects.
Species 1: Lepidotera Lymantriidae Lymantria dispar (gypsy moth)
Keywords: baculovirus, gypsy moth
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