ABSTRACT

The impact of Lygus bugs on cotton yield is poorly understood. Growers have long observed that there is a large amount of unexplained variability between the number of Lygus observed in a cotton field and the amount of damage the crop sustains. We have begun to investigate this phenomenon by asking the question: can differences in age structure and sex ratio among Lygus populations affect sampling accuracy and/or damage to cotton squares? In 2002 we documented a wide range of age structures (adults versus nymphs) and sex ratios (males versus females) across ten different Lygus populations in California. Experiments using "whole cage sampling" allowed us to examine the efficiency of sweep sampling for assessing the absolute age structures and sex ratios of these populations. Results suggest that sweep samples do predict Lygus presence, but that they are more efficient in capturing adults versus nymphs. The underestimation of nymphs due to sweep sampling bias presents a problem for Lygus management because nymphs feed on squares as much as (or more than) adults. Sweep nets were also more efficient in capturing adult males versus adult females. This underestimation of female adults may pose a similar problem for Lygus management because adult female Lygus spend more time feeding on squares relative to adult males. Adult female density was positively correlated with egg density, suggesting that the propensity of sweep nets to favor adult males could be an additional problem for predicting future generations of Lygus in a field.