D3132: Refuge realities: On-plant movement of western bean cutworm, Striacosta albicosta, in structured and integrated refuges in Ontario, Canada

Western bean cutworm (Striacosta albicosta (Smith; Lepidoptera: Noctuidae)) is a native pest of corn (Zea mays) and dry beans (Phaseolus vulgaris) in North America. The sole effective Bacillus thuringiensis (Bt) protein at controlling S. albicosta is Vip3A. As a highly mobile species, S. albicosta move from plant-to-plant throughout their lifespan which can result in sub-lethal exposures of Bt promoting resistance development when using integrated refuges. Monitoring for Vip3A resistance is critical to stewardship of Bt corn technology. Laboratory diet experiments conducted from 2022 to 2024 assessed the effect of various macronutrient ratios on the developmental rate and survival of S. albicosta. This research aimed to optimize artificial diets for S. albicosta rearing and Bt susceptibility monitoring. Neonate S. albicosta were placed into 30 gram cups containing 15 grams of artificial diet with four different protein-to-carbohydrate ratios, with assessments of survival and developmental time. Larval survival rates across treatments (0.5P:1.0C, 1.0P:1.0C, 1.5P:1.0C, and 2.0P:1.0C) were 23.3, 29.2, 15, and 2.5% respectively. In the second round of the experiment, adjustments to micronutrients increased survival rates in the 0.5P:1.0C and 1.5P:1.0C treatments to 87.5 and 36.7%, respectively. A subsequent diet treatment mimicked the protein-to-carbohydrate ratio experienced by S. albicosta in corn where 1st to 3rd instars consume mainly protein, to greater carbohydrate intake as 4th to 6th instars, resulting in 89.2% survival. Optimizing the larval diet of S. albicosta facilitates further research on Bt resistance development and other control strategies, aiming to mitigate economic losses for growers.