Novel host immune evasion strategy of the endoparasitoid Drino inconspicuoides.

The tachinid fly Drino inconspicuoides (Diptera: Tachinidae) is an ovolarviparous endoparasitoid whose larvae develop in the host haemocoel and avoids the host immune system. In this study, we investigated the immune evasion mechanisms of this species during infestation in the host Mythimna separata (Lepidoptera: Noctuidae). We discovered a unique 'cloak' that surrounded D. inconspicuoides larvae that penetrated into the host and determined through genomic polymerase chain reaction analysis that this structure originated from the host rather than the tachinid. The 'cloak' contained both haemocytes and fat body cells from the host, with the haemocytes assembling around the larvae first and the fat body cells then covering the haemocyte layer, following which the two mixed. Living D. inconspicuoides larvae that were wrapped in the 'cloak' were not melanized whereas encapsulated dead larvae were melanized, suggesting that this structure contributes to the avoidance of host immune reactions.