Effects of a protease-expressing recombinant baculovirus insecticide on the parasitoid Cotesia marginiventris (Cresson)

A recombinant baculovirus insecticide, AcMLF9.ScathL, has been constructed that expresses a cathepsin L-like protease. This protease degrades the basement membrane of infected-lepidopteran larvae. AcMLF9.ScathL kills larvae significantly faster than the wild type baculovirus. Before field trials can be conducted with this virus, risk assessment studies are required to examine the potential impact of the virus on nontarget organisms. We examined the impact of AcMLF9.ScathL on the survival, development, and behavior of the parasitoid Cotesia marginiventris (Cresson) that parasitizes infected second instar larvae. Larvae of Heliothis virescens were exposed to the parasitoid and infected with the wild type or recombinant virus at >LD99 at 72, 96, or 120 h after parasitism. Control larvae were mock infected. Choice tests showed that infection with AcMLF9.ScathL did not affect the host preference of the parasitoid. At 72 h post-parasitism, the survival of parasitoids emerging from hosts infected with AcMLF9.ScathL was lower than for parasitoids emerging from hosts infected with wild type virus or uninfected controls. There were no significant differences between AcMLF9.ScathL and wild type virus treatments for the larval emergence time, adult emergence time, sex ratio, size, and fecundity of C. marginiventris. These results indicate that use of AcMLF9.ScathL in insect pest management poses a slightly greater risk to the parasitoid at early stages of parasitoid development than use of the wild type virus at >LD99 dose.