Bean leaf beetle (Coleoptera : Chrysomelidae) abundance in soybean fields protected and unprotected by shelterbelts

The bean leaf beetle, Cerotoma trifurcata (Forster) (Coleoptera: Chrysomeli dae), is a major insect pest of soybean in Nebraska and throughout much of the Midwest. This insect overwinters in the adult stage in litter in wooded areas such as shelterbelts. Historically, crop producers have been unsure of the merits of shelterbelts, especially if nearby crops are more likely t o be infested by insect pests as a result. In this study, bean leaf beetle adults were sampled during the season by visually counting the number of be etles found on soybean plants early in the season and by sweep net sampling once plants were at the V4 stage (approximately 0.33 m tall). Sampling was done in 1997 and 1998 at the University of Nebraska Agricultural Research and Development Center in Saunders Co. in east-central Nebraska. Beetle cou nts were compared between shelterbelt-protected and -unprotected fields, in general, bean leaf beetles were more numerous in 1997 than in 1998, with a bundance peaks occurring in late-July and early-September in both years. Th ere were significant differences in bean leaf beetle counts from protected and unprotected fields on only three of the 11 and four of the 13 sampling dates in 1997 and 1998, respectively. On the sampling dates when significan t differences were found, two of three in 1997 and three of four in 1998 ha d higher bean leaf beetle abundance in the protected soybean fields. The re sults of this study indicate a tendency for more bean leaf beetles in shelt erbelt-protected soybean fields when differences are found, but beetle numb ers were not significantly different between protected and unprotected fiel ds on the majority of sample dates in the two years of this study. This stu dy also reconfirms the presence of two generations of the bean leaf beetle in Nebraska.