Bean leaf beetle (Cerotoma trifurcata) feeding preference and defoliation impact on snap beans

Bean Leaf Beetle Management in Snap Beans

The bean leaf beetle (BLB), Cerotoma trifurcata (Forster), is an important pest of legume crops in the eastern and central U.S. Adults feed on leaves and scar pods. The majority of research on this pest has focused on soybeans. On the Eastern Shore of Virginia, snap beans and lima beans are important crops along with soybeans, and relatively high populations of BLB occur. In 2007 and 2008, we conducted laboratory and field choice experiments to determine potential host plant preferences of BLB. In the lab, using paired leaf-disc bioassays, BLB consumed more leaf area of lima and snap bean over soybean. No differences were found between snap and lima bean. In field pairings of the aforementioned legumes, more beetles infested snap bean and lima bean plants over soybean. Results of both experiments suggest a host plant preference for snap bean and lima bean over soybean. An additional study was conducted to assess the effect of BLB leaf feeding on snap bean yield. We used a leaf-hole punch to remove 0, 25, 50 and 75 % of the total leaf area. Two groups were evaluated: the group one received two defoliation sessions, which imitated early-season defoliation pressure only, while the second group received four defoliation sessions, which represented season-long feeding pressure. Plants receiving 50% or more defoliation for both groups experienced significant yield losses as compared to the control. Regression analysis revealed a strong linear relationship between percentage defoliation and yield loss in snap beans.