Erin Hodgson, Department of Entomology and Rich Pope, Corn and Soybean Initiative
Although native to the U.S., bean leaf beetles have been only been considered an economic pest of soybean since the late 1980s. Adults feed on snap beans, dry beans, peas, alfalfa, clover and even corn, but strongly prefer soybean. Bean leaf beetle adults will feed on leaves, cotyledons, and pods, while the larvae feed on the roots; adult leaf-feeding injury is usually round or oval holes about the diameter of a pencil.
Populations of first and second generations of bean leaf beetle in Iowa have varied through the years, with widespread severe outbreaks seen in 2002 and 2005. Mild winters and persistent snow cover shelter overwintering adults, and earlier planting dates favor their egg-laying success. However, Iowa had an exceptionally harsh winter in 2008-2009, and predictive models suggest bean leaf beetles were hit hard. Based on accumulating subfreezing degrees, at least 73 percent of the adults could not survive regardless of the protective snow cover, as shown on the map below.
Bean leaf beetle adults can noticeably defoliate soybean seedlings, but rarely cause economic losses. Unfortunately, overwintering and first generation adults can spread bean pod mottle virus (BPMV), and lead to secondary infections on the developing pod. Bean leaf beetle management options include delayed planting to discourage heavy adult feeding and early-season virus transmission. Food-grade soybean and seed fields should be closely monitored for adults as soon as the plants emerge. Areas with high BPMV incidence should follow an integrated approach to reduce pod damage and improve seed quality (archived article here).
Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. Rich Pope is an extension program specialist in the Integrated Pest Management program.