Population Densities of Corn Flea Beetle (Coleoptera: Chrysomelidae) and Incidence of Stewart's Wilt in Sweet Corn

To quantify populations of the corn sea beetle, Chaetocnema pulicaria Melsheimer (Coleoptera: Chrysomelidae), and reÞne estimates of a threshold for its control to prevent StewartOs wilt caused by Erwinia stewartii, sequential plantings of OJubileeO sweet corn were made at 2-wk intervals from April or May through August or September 2001 and 2002 at four locations from southern to northern Illinois: Simpson, Brownstown, Champaign, and Mendota. Densities of C. pulicaria and incidence of StewartOs wilt were monitored weekly. At Mendota, where C. pulicaria populations were decimated by cold temperatures during winter 2000 Ð2001, densities reached 33.3 beetles per 15-cm yellow sticky trap per day by September 2002, after a mild 2001Ð2002 winter. Maximum incidence of StewartOs wilt in single plots at Simpson, Brownstown, Champaign, and Mendota was 22, 36, 39, and 2%, respectively, in 2001, and 33, 47, 99, and 87%, respectively, in 2002. In 24 plots where beetle densities were 2 per trap per day, StewartOs wilt incidence was 5% in 20 plots. We propose that two corn sea beetles per trap per day be used as a threshold for insecticide application to seedlings to control C. pulicaria and minimize subsequent incidence of StewartOs wilt in processing sweet corn. Enzyme-linked immunosorbent assays indicated that E. stewartii incidence in C. pulicaria peaked at 67, 62, and 54%, respectively, at Simpson, Brownstown, and Champaign, in 2001, and at 71, 76, and 60%, respectively, in 2002. Further studies might allow the use of areawide or Þeld-speciÞc estimates of E. stewartii incidence in corn sea beetles for adjusting management decisions.