Baseline susceptibility and resistance monitoring of Striacosta albicosta (Lepidoptera: Noctuidae) Vip3A, a Bacillus thuringiensis protein, and foliar insecticides
Striacosta albicosta (Smith) (Lepidoptera: Noctuidae) is an emerging pest of corn (Zea mays L.) in the Great Lakes region. In the past fifteen years, S. albicosta has experienced a rapid range expansion, moving from Nebraska to the Maritime Provinces of Canada. Larvae of S. albicosta feed on corn causing economic damage and the potential for mycotoxin contamination. Transgenic corn expressing the Bacillus thuringiensis (Bt) vegetative insecticidal protein Vip3A and foliar insecticides are recommended for the management of S. albicosta; however, with the development of S. albicosta resistance to Cry1F Bt protein, resistance management is of concern for many researchers, corn producers, and product developers. The objective of this research was to determine the susceptibility and degree of exposure of S. albicosta larvae to these technologies. First instar S. albicosta were very susceptible to Vip3A protein and foliar insecticides. However, the susceptibility of older instars of S. albicosta to these technologies was lower than 1st instars. The estimated exposure of S. albicosta instars to Vip3A and foliar insecticides varied greatly depending on corn tissues assessed. First instar S. albicosta are likely to be exposed to high doses of Vip3A and foliar insecticides under field conditions; however, older instars may not be exposed to high doses of Vip3A and foliar insecticides under the same conditions. Specific to Vip3A, corn tissue assays showed higher survival of later instars of S. albicosta on various corn tissues, and developmental measures such as larval weights, body length, and head capsule width, of larvae that were exposed to Vip3A-expressing tissues did not differ from those exposed to the control. Specific to foliar insecticides, the persistence of each insecticide in the field after application varied greatly. The results of this research suggest management of 1st instar S. albicosta with Vip3A and foliar insecticides is achievable; however, using these technologies, control may not be sufficient to prevent damage by older S. albicosta instars that can cause potential for mold infection.