Sweep net recapture of marked Lygus hesperus Knight (Hemiptera: Miridae) adults after different release times in cotton

Authors: Cooper, William - Rodney; Spurgeon, Dale

Submitted to: Journal of Cotton Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2010
Publication Date: 11/12/2010
Citation: Cooper, W.R., Spurgeon, D.W. 2010. Sweep net recapture of marked Lygus hesperus Knight (Hemiptera: Miridae) adults after different release times in cotton. Journal of Cotton Science. 14:131-137.

Interpretive Summary: Although the sweep net is a standard method for sampling the western tarnished plant bug in cotton, the relationship between numbers of bugs captured and actual populations is poorly understood. Methods in which marked bugs are released and then sampled have been developed to address this question, but the most appropriate duration between release and sampling has not been determined. We conducted two studies to determine the effects of bug release time on sampling effectiveness of the sweep net. The first study used two release times and indicated more marked bugs were recaptured when they were released 2 hours before sampling than when they were released on the evening before sampling. Observations of plant development suggested that releases 2 hours before sampling did not provide sufficient time for bugs to move away from the points of release. The second study, which used three release times, indicated more marked bugs were recaptured when they were released <5 minutes before sampling than when they were released 2 hours before or on the evening before sampling. However, in the second study, predators were observed to remove many marked bugs before they could be sampled. Our results indicate that future studies should incorporate procedures that allow sufficient time for marked bugs to move from the release points to locations on plants normally occupied by wild bugs. Furthermore, studies should be designed such that high population levels of plant bug predators are avoided or controlled.

Technical Abstract: The elevated status of Lygus spp. as key cotton pests has accentuated the need for improved interpretation of population samples. Mark-release-recapture methods were recently developed to investigate factors that affect sweep net sampling of adult L. hesperus. During these efforts, marked bugs were released in the evening before sampling the following morning. Releases closer to the time of sampling would provide greater flexibility in future mark-release-recapture studies, but the effects of release time on subsequent recapture is unknown. Our objective was to compare sweep net collections of marked bugs following different release times. Separate studies were conducted in two plantings of Acala cotton (Gossypium hirsutum). In the first planting (study 1), marked bugs were released into rows on the evening before sampling or 2 hours before sampling. In the second planting (study 2), we included an additional release <5 minutes before sampling. In study 1, more marked bugs were recaptured from rows in which bugs were released 2 hours before sampling than from rows in which bugs were released on the evening before sampling. This difference was not repeated in study 2, but more bugs were recaptured from rows in which bugs were released <5 minutes before sampling compared with other releases. Based on differences in plant development and observed predation between the two plantings, we hypothesize that the affects of release time on the recapture of marked bugs were caused by increased within-plant redistribution of marked bugs and by increased losses to predation with increased time between releases and sampling.