Lethal effects of insecticides against adults of Macrosaccus morrisella through multiple exposure routes

Macrosaccus morrisella (Fitch) (Lepidoptera: Gracillariidae) is a tiny leaf-mining insect native to North America. This insect was recently first reported feeding on soybean in Canada and the U.S. However, control methods for the management of this pest are still unknown. In this context, a study was developed with the objective of evaluating the lethal effects of two insecticides against male and female adults of M. morrisella through multiple exposure routes. Adults of a laboratory colony were exposed to Agri-Mek (abamectin) and Endigo ZCX (thiamethoxam + lambda-cyhalothrin) through residual contact exposure, oral exposure, or a combination of residual contact exposure and oral exposure routes. Adult mortality was assessed daily, and insects were preserved after death for sexing under a dissecting microscope. The survival of males and females did not differ within treatments; therefore, sexes were pooled for further analyses. The survival of adults exposed to either insecticide through oral exposure or the combination of residual contact exposure and oral exposure was significantly lower than that of residual contact exposure and the untreated control. Residual contact exposure to the mixture of thiamethoxam and lambda-cyhalothrin was intermediate between the untreated control and treatments including oral exposure to either insecticide. Within each exposure route, the response to the two insecticides did not differ. These results show that abamectin and the mixture of thiamethoxam and lambda-cyhalothrin may have potential for the control of M. morrisella, but further work is needed to evaluate efficacy against immature stages of this pest.