Economic injury levels and sequential sampling plans for Mexican bean beetle (Coleoptera: Coccinellidae) on dry beans

Field studies were conducted during the growing seasons of 1995 and 1996, in Scotts-bluff, Nebraska, to determine yield-loss relationships for Mexican bean beetle (Epilachna varivestis Mulsant) on dry bean (Phaseolus vulgaris L.). Results of those experiments were combined with data from other studies previously conducted to develop economic injury levels (EILs), economic thresholds (ETs), and a sequential sampling program for Mexican bean beetle. Yield loss was regressed against larvae/row-m, and the slope of the linear regression (113 kg/ha per larvae/row-m) was used as the DI (yield loss/insect density) variable in EIL calculations. The EILs calculated in larvae/row-m were converted to egg masses/row-m and adjusted to reflect average survivorship to the adult stage. An example EIL for esfenvalerate at 0.509 (formulation) liter/ha (0.0453 gal/a) and crop value of 0.44 dollars/kg (20 dollars/100 lbs) was 17.78 larvae/row-m. The corresponding ET is 1.04 egg masses/row-m, which reflects an average of 54.6 eggs/egg mass and 33% survival rate from egg to injurious stages. Sequential sampling plans were calculated based on a negative binomial distribution using parameter k estimated from previous research. Because sampling is based on egg masses, growers can make management decisions and take management actions before significant injury occurs. Also, ETs can be adjusted to include the occurrence of natural mortality in the egg and early instars. Analyses demonstrated that relatively minor variation in ETs has substantial impact on sequential sampling plans, including parameters such as average sample number. An interactive spreadsheet was developed that allows users to input economic and other data specific to their situation to calculate Mexican bean beetle EILs, ETs, and sequential sampling plans.