Estimating Absolute Density of Nymphs of Lygus lineolaris (Heteroptera: Miridae) in Cotton Using Drop Cloth and Sweep-Net Sampling Methods

Abstract

The efficiencies of the drop cloth and sweep net for capturing tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), nymphs were determined by, sampling nymphs placed on cotton each week during the first 5-6 wk of fruit production. Capture efficiency for both sampling methods was compared with plant height by regression analysis, and significant regression values were 0.72 for the drop cloth and 0.58 for the sweep net. The accuracies of the regression equations obtained were tested by sampling a natural infestation of tarnished plant bugs in a cotton field at Stoneville, MS, in 1990 and 1991 during the first 5 wk of fruit production. The actual nymphal population present in the field was estimated using absolute samples, and by correcting counts from sweep-net and drop-cloth samples using the regression equations for sample efficiency. Percentage agreement between numbers of nymphs captured in the absolute samples and in corrected drop cloth samples was 84.2% (92.8%during the first 3 wk) in 1990; in 1991 it was 83.2% (87.5% during the first 3 wk). The regression equation for sweep-net efficiency did not satisfactorily correct nymphal numbers, and only 36.4 and 40.5% of the corrected number were found in the absolute samples in 1990 and 1991, respectively. Accuracy of the drop cloth counts, taken during the first 3 wk of fruit production and corrected by the regression equation, should be adequate for researchers and producers to determine infestation rates of plant bug nymphs in cotton.