Phenology, herbivory, and bioeconomics of the bean leaf beetle on soybean
Bean leaf beetle, Cerotoma trifurcata (Forster), adult sampling studies in alfalfa and soybean during 1986, 1987 and 1988 revealed that this insect produces two generations per year in central Iowa. Diurnal sampling (excluding nighttime hours) indicated that adult abundance is least before 1000 h or during a period of appreciable dew on the canopy;Artificial infestation research in caged soybeans near Ames, IA, during late season of 1986, 1987 and 1988 revealed that bean leaf beetle adults fed on leaves, outer surfaces of pod and stem tissue, and clipped pods simultaneously during mid-August to mid-September. Injury per beetle was quantified for each type of feeding;Regression analysis of yield parameters revealed that a 3.06 kg/ha yield loss was caused by each bean leaf beetle per square meter. Information from this analysis also indicated that 685 to 1076 injured pods/m[superscript]2 were necessary for sufficient seed damage to incur an economic discount. Official damaged seed weight per injured pod seemingly was dependent on late-season rainfall;Economic-injury level equations were determined for late-season bean leaf beetle pod injury. Analyses revealed that economic-injury levels based on seed-yield loss are exceeded before economic penalties are incurred from damaged seed in surface-injured pods. Bean leaf beetle adult and injured-pod dispersion analysis using Iowa's regression and Taylor's power law analyses indicated that the adults are significantly aggregated, but injured pods are randomly distributed. Sequential count plans were developed for bean leaf beetle-adult and injured-pod sampling.