Conservation risks and benefits of establishing monarch butterfly (Danaus plexippus) breeding habitat in close proximity to maize and soybean fields in the North Central U.S.: A landscape-scale analysis of foliar insecticide impacts on non-migratory monarch butterfly populations.

Establishing habitat in agricultural landscapes of the north central U.S. is critical to reversing the decline of North America's eastern monarch butterfly (Danaus plexippus) population. Insecticide use could create population sinks and threaten recovery. Discouraging habitat establishment within a 38-m zone around crop fields is a suggested risk mitigation measure. In Story County, Iowa, this mitigation would discourage habitat establishment in 84% of roadsides and 38% of non-crop land. It is unclear if conservation benefits from establishing habitat in close proximity to crop fields outweigh suppression of population growth due to insecticide exposure. Consequently, monarch conservation plans require spatially and temporally explicit landscape-scale assessments. Using an agent-based model that incorporates female monarch movement and egg laying, the number and location of eggs laid in Story County were simulated for four habitat scenarios: current condition; maximum new establishment; moderate establishment; and moderate establishment only outside a 38-m 'no plant zone' around crop fields. A demographic model incorporated mortality from natural causes and insecticide exposure to simulate adult monarch production over 10 years. Assuming no insecticide exposure, simulated adult production increased 24.7% and 9.3%, respectively, with maximum and moderate habitat establishment and no planting restrictions. An increase of 3.5% was simulated assuming moderate habitat establishment with a 38-m planting restriction. Impacts on adult production were simulated for six representative insecticides registered for soybean aphid (Aphis glycines) management. Depending on the frequency of insecticide applications over a 10-year period, simulated production increased 8.2% to 9.3%, assuming moderate habitat establish with no planting restrictions. Results suggest benefits of establishing habitat in close proximity of crop fields outweigh adverse effects of insecticide spray drift; i.e., metapopulation extirpation is not a concern for monarchs. These findings are only applicable for species that move at spatial scales greater than the scale of potential spray drift impacts. This article is protected by copyright. All rights reserved.