Captures of boll weevils (Coleoptera: Curculionidae) in relation to trap orientation and distance from brush lines

Authors: Spurgeon, Dale

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2015
Publication Date: 4/12/2016
Publication URL: http://handle.nal.usda.gov/10113/62311
Citation: Spurgeon, D.W. 2016. Captures of boll weevils (Coleoptera: Curculionidae) in relation to trap orientation and distance from brush lines. Journal of Economic Entomology. 109(2):676-683. doi: 10.1093/jee/tov392.

Interpretive Summary: Boll weevil eradication programs rely almost entirely on traps baited with an attractive odor (pheromone) to determine the need for insecticide treatment and to judge progress towards eradication. In the later years of eradication efforts, a key objective of trapping is to minimize control costs by detecting boll weevils while population levels are still low. Therefore, improvements in the effectiveness of trapping would enhance efforts to achieve and maintain boll weevil eradication. An ARS scientist at Maricopa, AZ, demonstrated that captures of weevils by traps placed away from brush were often influenced by trap distance from the brush. However, these differences between distances depended on whether the traps were upwind or downwind from the brush, and upon wind speed and wind direction. In contrast, traps placed directly on the edge of brush lines consistently caught higher numbers of boll weevils than traps away from brush, irrespective of wind direction. Furthermore, when weevil populations were very low, traps placed on the edge of brush were up to 30% more likely to capture one or more weevils than traps placed away from brush. These results illustrate the importance of trap placement in efforts to maximize the effectiveness of trap-based boll weevil monitoring in support of eradication.

Technical Abstract: Eradication programs for the boll weevil (Anthonomus grandis Boheman) rely on pheromone-baited traps to trigger insecticide treatments and monitor program progress. A key objective of monitoring in these programs is the timely detection of incipient weevil populations to limit or prevent re-infestation. Therefore, improvements in the effectiveness of trapping would enhance efforts to achieve and maintain eradication. Association of pheromone traps with woodlots and other prominent vegetation are reported to increase captures of weevils, but the spatial scale over which this effect occurs is unknown. The influences of trap distance (0, 10, 20 m) and orientation (leeward, windward) to brush lines on boll weevil captures were examined during three non-cropping seasons (October to February) in the Rio Grande Valley of Texas. Differences in numbers of captured weevils and in the probability of capture between traps at 10 or 20 m from brush, although often statistically significant, were generally small and variable. Variations in boll weevil population levels, wind directions, and wind speeds apparently contributed to this variability. In contrast, traps closely associated with brush (0 m) generally captured larger numbers of weevils, and offered a higher probability of weevil capture compared with traps away from brush. These increases in the probability of weevil capture were as high as 30%. Such increases in the ability of traps to detect low-level boll weevil populations indicate trap placement with respect to prominent vegetation is an important consideration in maximizing the effectiveness of trap-based monitoring for the boll weevil.