Induced resistance to bean leaf beetle (Coleoptera: Chrysomelidae) in soybean

Induced resistance in soybean, Glycine max (L.) Merrill, to the bean leaf beetle, Cerotoma trifurcata (Forster), was investigated in greenhouse experiments using the treatments of mechanical injury, a chemical inducer (Actigard (TM), Novartis Crop Protection Inc., Greensboro, NC) and defoliation by the bean leaf beetle and the soybean looper, Pseudoplusia includens (Walker). Experiments were conducted on soybean PI 227687, two soybean cultivars (Colfax and Williams 82) and a soybean germplasm line (HC95-24MB). Dual-choice feeding-preference tests with bean leaf beetle adults were used to assess induced resistance. Adult beetles were collected from soybean fields 2 to 5 d prior to the feeding preference tests. Pairwise comparisons of leaflets from treated and untreated (control) plants indicated that soybean looper herbivory was a better inducer than other treatments. Herbivory by bean leaf beetle feeding and Actigard following artificial defoliation also were found to induce resistance to the bean leaf beetle. Mechanical injury alone elicited a significantly lower induced response in plants than the other induction treatments.