Larvae of the tachinid fly,Drino inconspicuoides (Diptera: Tachinidae), suppress melanization in host lepidopteran insects

The ovoviviparous parasitoid, Drino inconspicuoides (Diptera: Tachinidae) parasitizes a wide range of lepidopteran insects; larval period progresses in the host hemocoel. Here, we examined how D. inconspicuoides responds to melanization, which involves the activation of prophenoloxidases and is the first immune reaction induced by the host against invading organisms. We found that the larvae of D. inconspicuoides suppressed the activation of prophenoloxidases in its natural hosts, Mythimna separata (Lepidoptera: Noctuidae) and Bombyx mori (Lepidoptera: Bombycidae). The suppression of melanization starts immediately after invasion and is maintained for at least 24 h. We did not detect a drastic degradation of prophenoloxidases, suggesting that the presence of other molecules targeted by D. inconspicuoides suppresses melanization. D. inconspicuoides does not inhibit a cellular immune reaction, encapsulation, and thus, it is likely that the tachinids survive secondary infections of the host by partially retaining the host immune function.