Since insects are vectors for many parasitic diseases of humans and animals, understanding the interactions between parasites and their insect hosts is an important area of study. Critical to the development of many endoparasites is abrogation or evasion of the host immune response. However, the mechanisms by which parasites overcome insect immune responses remain obscure. We propose to examine the mechanism by which a parasite compromises the host immune system in a unique insect model system. We have found that the polydnavirus from the parasitic wasp Microplitis demolitor suppresses the encapsulation response of the wasp's lepidopteran host, Pseudoplusia includens. The presence of the virus is essential to the survival of the developing parasite, because the wasp is quickly encapsulated by the host if the virus is absent. Physiological studies suggest the host's inability to encapsulate the parasite is associated with alterations in specific types of blood cells (hemocytes). Nucleic acid hybridization experiments indicate that M. demolitor polydnavirus (MdPDV) DNA is present in host hemocytes, and MdPDV specific transcripts are detectable in hemocytes within 4 h of injecting MdPDV into the host. Further, higher levels of MdPDV expression are associated with hemocytes than any other host tissue. The objectives of this proposal are fourfold. First, we will characterize the persistence and expression of MdPDV in host hemocytes by Southern, Northern and in situ hybridization. Second, we will identify and characterize MdPDV RNAs from infected P. includens hemocytes using our already established MdPDV genomic library and/or a cDNA library approach. Third, we will determine whether venom from the adult wasp interacts with host hemocytes or in some way facilitates entry of MdPDV into host hemocytes. The interaction of venom with hemocytes and/or MdPDV will be characterized using antibodies already generated against venom components. Fourth, we will examine the physiological effects of MdPDV on the host immune response in vivo and in vitro. Attention will be focused on whether the altered response of hemocytes is due to factors present in plasma or to intrinsic alterations in hemocytes themselves. We also will determine whether the alterations in the host immune response are specific to the parasite or more general. The long-range goals of the study are to understand the basis by which insect parasites affect the host immune system and to gain insight into the invertebrate immune response.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
Project #
Application #
Study Section
Tropical Medicine and Parasitology Study Section (TMP)
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Wisconsin Madison
Schools of Earth Sciences/Natur
United States
Zip Code
Harvey, Jeffrey A; Gols, Rieta; Strand, Michael R (2009) Intrinsic competition and its effects on the survival and development of three species of endoparasitoid wasps. Entomol Exp Appl 130:238-248
Kadash, K; Harvey, J A; Strand, M R (2003) Cross-protection experiments with parasitoids in the genus Microplitis (Hymenoptera: Braconidae) suggest a high level of specificity in their associated bracoviruses. J Insect Physiol 49:473-82
Lavine, M D; Strand, M R (2002) Insect hemocytes and their role in immunity. Insect Biochem Mol Biol 32:1295-309
Trudeau, D; Witherell, R A; Strand, M R (2000) Characterization of two novel Microplitis demolitor polydnavirus mRNAs expressed in Pseudoplusia includens haemocytes. J Gen Virol 81:3049-58
Strand, M R; Witherell, R A; Trudeau, D (1997) Two Microplitis demolitor polydnavirus mRNAs expressed in hemocytes of Pseudoplusia includens contain a common cysteine-rich domain. J Virol 71:2146-56
Strand, M R; Pech, L L (1995) Immunological basis for compatibility in parasitoid-host relationships. Annu Rev Entomol 40:31-56
Strand, M R; Pech, L L (1995) Microplitis demolitor polydnavirus induces apoptosis of a specific haemocyte morphotype in Pseudoplusia includens. J Gen Virol 76 ( Pt 2):283-91
Strand, M R; Johnson, J A; Noda, T et al. (1994) Development and partial characterization of monoclonal antibodies to venom of the parasitoid Microplitis demolitor. Arch Insect Biochem Physiol 26:123-36
Pech, L L; Trudeau, D; Strand, M R (1994) Separation and behavior in vitro of hemocytes from the moth, Pseudoplusia includens. Cell Tissue Res 277:159-67
Strand, M R (1994) Microplitis demolitor polydnavirus infects and expresses in specific morphotypes of Pseudoplusia includens haemocytes. J Gen Virol 75 ( Pt 11):3007-20