Movement of Striacosta albicosta (Smith) (Lepidoptera: Noctuidae) Larvae on Transgenic Bt and Non-Bt Maize

SIMPLE SUMMARY: The planting of genetically modified crops that express insecticidal proteins is central to modern pest management, particularly for maize and cotton in the United States. An understanding of how the presence of transgenic proteins can affect the movement and feeding behavior of insect pests will allow us to better design resistance management strategies to prolong the use of this technology. In this study, the western bean cutworm, a regionally important pest of maize, was studied in artificial arena and on-plant experiments. Two more artificial experiments did not indicate significant changes to young caterpillar behavior when exposed to maize tissues expressing transgenic proteins; however, the more field-realistic and longer exposure period studies did indicate that young caterpillars would abandon plants that expressed transgenic proteins more often that those that did not. This finding has particular importance for the use of integrated versus structured refuges. ABSTRACT: Exposure of lepidopteran pests to Bacillus thuringiensis (Bt) proteins has been shown to affect the behavior of larvae, including increased movement and avoidance of Bt-expressing plants or diet. Therefore, we hypothesized that the behavior of western bean cutworm, Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), an important pest of maize, could be affected when exposed to Bt plants. To test this hypothesis, we conducted a series of artificial arena and on-plant experiments to determine S. albicosta neonate behavior when exposed to Bt and non-Bt plant tissue. Video tracking experiments presented neonate larvae with the choice of Bt or non-Bt pollen in a Petri dish for 15 min while being video recorded for analysis with EthoVision software. This study showed an increase in mean velocity and total time spent moving for larvae in the presence of Cry1F vs. non-Bt when compared with Vip3A vs. non-Bt or Cry1F vs. Vip3A. However, there was no difference in total distance moved or time spent in the food zone for all scenarios. Maize tissue choice experiments allowed neonatal larvae the choice of feeding on Bt or non-Bt tassel or leaves for 9 h in Petri dish arenas. This experiment showed that larvae preferred tassel tissue over leaves but did not indicate that larvae could distinguish between Bt and non-Bt tissue. In contrast, on-plant experiments (including a whole plant neonate dispersal study under controlled conditions and an in-field silking behavior experiment) indicated that the presence of Cry1F and Vip3A Bt toxins increased plant abandonment, suggesting that larvae are able to detect and avoid Bt toxins. The discrepancy of these results is likely due to the on-plant studies providing more field-realistic environmental conditions and a longer duration of exposure to Bt toxins for the behavioral experiments. Our results represent the first steps in understanding the complex behavior of S. albicosta when exposed to Bt plants. A better understanding of the response of larvae when exposed to Bt traits can aid in the management of this pest, particularly for the design of resistance management strategies and refuge design.