COMPARISON OF SAMPLING TECHNIQUES FOR GRASSHOPPERS (ORTHOPTERA, ACRIDIDAE) IN SOYBEAN

A 2-yr study was conducted for evaluating sampling techniques for the grasshoppers Melanoplus femurrubrum (De Geer) and M. differentialis (Thomas) in soybean. Objectives were to establish a technique for obtaining absolute estimates of density and to evaluate the potential for calibrating the sweep net (relative density estimates) for absolute density estimates. Assessments of absolute density were made at night by using a cage-bag method. Sweep samples were collected during both day and night. Night sweeping was more effective than day sweeping for capturing grasshoppers. Regression results of relative on absolute estimates for nymphs indicated that both day and night sweeps adequately reflected population change. In contrast, similar analyses for adults indicated sufficient fidelity for night sweeps only. Day or night, fidelity of sweeps was better for M. femurrubrum than for M. differentialis. Regression coefficients were significantly different between nymphs and adults, but not between species. Therefore, combined-species regression models were formulated for nymphs (day and night) and for adults (night). Satisfactory fidelity of species-specific and combined-species day (nymphs) and night (nymphs and adults) models warrants the use of these models for calibration. Despite both day and night sweeps being biased in estimating age-class structure for nymphs, nymphal models are useful for management.