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ViewAttendees 10

P-IE

10-Minute Paper

10-min: P-IE, IPM

Modeling landscape-scale effects of insecticide drift on monarch butterfly (Danaus plexippus) populations in an Iowa agroecosystem to support a national assessment

On-Demand
On-Demand
Spray drift from foliar insecticide application causing mortality in monarch butterfly (Danaus plexippus) larvae near agricultural fields is considered a threat to population recovery in the draft U.S. FWS national species status assessment. Assessing risks to vagile species like monarch butterflies requires modeling adult movement, larval development, and insecticide application at landscape scales. In Iowa, foliar insecticides are used to control late season soybean aphids (Aphis glycines) and early season true armyworms (Mythimna unipuncta).  Previously published laboratory studies conducted to determine the 96-hour cuticular and dietary larval mortality dose-response curves for beta-cyfluthrin, chlorpyrifos, imidacloprid, thiamethoxam, chlorantraniliprole and clothianidin indicate that larval mortality after a spray drift event may be high in downwind common milkweed (Asclepias syriaca) patches; however, landscape-scale effects on non-migratory monarch populations have not been estimated.  We combined the power of an agent-based model, a recently developed statistical model to estimate larval survival, and comprehensive laboratory studies of insecticide mortality to simulate the effect of spray drift on a landscape-scale monarch population in Story County, Iowa.  The agent-based model simulated monarch egg-laying on the Story County landscape. A demographic model, incorporating natural mortality and insecticide-caused mortality, simulated the number of adult monarchs produced. The insecticides causing the most mortality from combined cuticular and dietary exposure, were, in order of severity:  chlorantraniliprole, chlorpyrifos, beta-cyfluthrin, clothianidin, imidacloprid, and thiamethoxam. Results indicate that despite some mortality from spray drift, augmenting milkweed adjacent to agricultural fields results in a net benefit to monarch populations.