Effect of systemic imidacloprid on the parasitism rates of the tobacco budworm, Heliothis virescens, by Toxoneuron nigriceps and Campoletis sonorensis in flue-cured tobacco

The hymenopteran parasitoids Cardiochiles nigriceps and Campoletis sonorensis are prevalent throughout the tobacco growing regions of the Southeastern United States.  These two species are valued as economical biological tools in controlling tobacco budworm infestations.  The use of the systemic insecticide imidacloprid has become an industry standard in tobacco production for its early season control and deterrence of sucking pests and concomitant reductions in incidence of Tomato Spotted Wilt Virus infections.  The toxicological and sublethal effects of imidacloprid to Hymenopteran species are well described in scientific literature.  However, the potential for negative consequences due to the developmental exposure of endoparasitoids has been largely ignored.  This study examines how the rate of tobacco budworm infestations and parasitism are affected through the use of systemic imidacloprid in flue-cured tobacco.  In field trials, parasitism rates were negatively affected when the time budworm larvae spent feeding on treated plants was maximized.  Plots treated with imidacloprid had higher infestation rates of older, and thus more damaging, budworm larvae.  When repeated in the greenhouse, this same study showed a greater difference between treatments with a higher rate of successful parasitism events in untreated plants.  The potential differences in the toxicological affects to both species and plans for future experiments are discussed.