Effect of Cry1F corn on larval feeding and movement of susceptible and resistant fall armyworm (Spodoptera frugiperda)

Understanding the behavior of pests targeted with Bacillus thuringiensis Berliner transgenic crops is important to define resistance management tactics. Particularly, the study of larval movement between plants is important to better understand feasibility of different refuge configurations. Studies have shown that exposure to Bt corn seems to increase larval movement in some lepidopteran species. However, few studies have examined the potential for resistance to interact with behavioral responses to Bt toxins. Choice and no-choice experiments were conducted with Spodoptera frugiperda (J. E. Smith) to determine if Cry1F resistance influences neonate movement. Leaf discs of TC1507 corn and the corresponding isoline were used to identify behavioral responses. The position of the larvae was recorded for five days, after which the leaf discs were scanned to estimate consumption. Percentage of larvae on leaves ≤7h exposure was used to analyze feeding preference to avoid mortality effects. In choice experiments, approximately 50% of resistant and susceptible phenotypes selected Bt tissue indicating that both phenotypes choose plants randomly. A small percentage of the susceptible phenotype abandoned Bt tissue, with nearly 80% remaining on Bt leaf discs. The non-choice experiment showed that resistant and susceptible phenotypes remained on the leaf regardless of food resource. These results differ from the behavior reported in other lepidopteran pests, more likely to move away from Bt corn. These results may help to evaluate the utility of integrated refuge for fall armyworm.