Calibration of Ground Cloth and Sweep Net Sampling Methods for Larvae of Corn Ear worm and Soybean Looper (Lepidoptera: Noctuidae) in Soybean

Abstract

Ground cloth and sweep net methods were used to estimate population levels of larvae of laboratory-reared Helicoverpa zea (Boddie) and Pseudoplusia includens (Walker) (Lepidoptera: Noctuidae) on hand-infested soybean (Glycine max (L.) Merrill) plants under field cages. Instar, plant growth stage, row spacing, and time of day effects were examined. Ground cloth and sweep net population estimates were calibrated against absolute estimates of instars and total larvae for both species. Linear regressions indicated that ground cloth and sweep net estimates were closely related to absolute estimates for both species in most cases. Slopes of regression lines for the ground cloth tended to be higher than those for the sweep net, indicating that the ground cloth more efficiently extracted larvae from the plants. The sweep net method, when used to sample H. zea larvae, appeared to be affected by plant growth stage. Row spacing had little effect on population density estimates obtained with the sweep net except in the case of P. includens on vegetative stage plants. No time-of-day effect was observed for P. includens with either sampling method.