Parasitoid-induced alteration of the immune response of Lymantria dispar larvae to permissive and nonpermissive microsporidian infections

In the proposed research project we will study the role of the immune response of Lymantria dispar larvae in an infection with entomopathogenic microsporidia. Larvae will be infected with various microsporidian isolates to which L. dispar is either a permissive or a nonpermissive host. The course of the infections by these isolates and signs of host defense reactions will be studied using light microscopy, the response of the host hemocytes will be quantified, the role of hemocytes, for the spread of microsporidian infection evaluated, and phenoloxidase activity in the hemolymph will be measured. In a next step we will employ a symbiotic polydnavirus and venom of a parasitic wasp to suppress the immune system of the L. dispar larvae. The course of infections with microsporidia which normally elicit permissive and nonpermissive responses in the host, respectively, will be studied in immune compromised hosts and untreated hosts, both after oral ingestion of infective spores and after transfer of hemocytes or infested tissue from infected larvae. Moreover, we will test whether a compromised immune system allows sufficient production of infective spores in normally nonpermissive hosts to enable horizontal transmission of the infection to conspecific larvae.