Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 27, 2002
Publication Date: N/A
Interpretive Summary: Traps baited with a chemical (pheromone) that attracts boll weevils are often used to guide decisions on whether to treat nearby fields with insecticides, but variation in numbers captured between traps and between days can be very high, making interpretation difficult. A possible source of this variation may arise if traps interfere with each other when they are placed too close together, presumably because the odor plumes from the different traps overlap. Experiments showed that five traps spaced 15 m or 20 m apart do interfere with one another if the wind is of moderate speed (10-20 km/h) and if it is striking the trap line at an angle more than 22 degrees away from the perpendicular. The most common effect is that the trap furthest upwind captured more weevils than the other traps in the line. The trap second furthest upwind tended to capture the fewest weevils.
Technical Abstract: Traps baited with the synthetic aggregation pheromone of the boll weevil (Anthonomus grandis) 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 if five traps placed in a line at two commonly used spacings (15 m 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 away from the perpendicular. The largest and most consistent effect was that the trap furthest upwind in the line captured the most weevils. 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 capture of any of the traps. Placement of the trap line on the leeward or windward side of a brush line did not affect this pattern.