Parasitic wasp virus infection inhibits encapsulation but not phagocytosis by host hemocytes

Encapsulation and phagocytosis are two of the primary cellular defenses employed by insect hemocytes in response to insult by parasites, microbes, or other foreign agents. The Diachasmimorpha longicaudata entomopoxvirus (DlEPV) is introduced into Anastrepha suspensa larvae during parasitism by the D. longicaudata female wasp. DlEPV along with a rhabdovirus (DlRhV) invade and replicate in the host's hemocytes. DlRhV subsequently migrates to the host's epidermal cells but DlEPV persists in the hemocytes. The objectives of this study were to determine (1) the temporal sequence and mechanism of infection by DlEPV and (2)the impact of infection on encapsulation and phagocytosis by hemocytes. Transmission electron microscopy and 3D confocal immunofluorescence microscopy revealed that DlEPV invades hemocytes within 12 h post parasitism (hpp) when the viral envelope adheres to and coalesces with hemocyte plasma membrane and within 48-72 hpp, extracellular enveloped virus (EEV) are released to infect new hemocytes. Flow cytometry of infected and control hemocytes of 24, 48, and 72 hpp, revealed that fluorescent beads (<1mm) coated with Escherichia coli lysates were phagocytosed by >80% of infected and control hemocytes but that 95% of infected hemocytes were unable to encapsulate sephadex beads of various sizes compared to 100% of controls that could. Thus, hemocytes retain their ability to protect against bacterial infection despite their inability to eliminate larger invaders such as wasp parasite eggs and larvae.