Mutual interference of pheromone traps within trap lines on captures of boll weevils (Coleoptera: Curculionidae)

Abstract

Traps baited with the synthetic aggregation pheromone of the boll weevil (Anthonomus grandis Boheman) are often used to monitor population fluctuations, distribution, and behavior. However, many factors generate variability in daily captures, making interpretation of trapping data difficult. Previous studies have shown that wind speed in the microenvironment around a trap can greatly affect numbers captured on a given day. It is possible that variation in air movement may also generate variation in trap captures through its effects on the pheromone plume. The current study was conducted to determine whether five traps placed in a line at two commonly used spacings (15 and 20 m) interfere with one another. There was no evidence for interference on days when winds struck the trap line at a nearly perpendicular angle. However, for both spacings, there were significant and substantial effects of relative trap placement within a line on days when winds struck it at an angle (>22.5°) away from the perpendicular. The largest and most consistent effect was that the trap furthest upwind in the line captured the most weevils, especially on days of moderate wind speeds (10-20 km/h). The upwind trap captured 1.5-2.0 times as many weevils as the next trap in the line, which usually had the lowest percentage of capture of any of the traps. Until the minimum adequate spacing has been established, traps should be placed at least 30 m apart in experíments in which such biases can adversly affect interpretation of results.