Variation in boll weevil (Coleoptera: Curculionidae) captures in pheromone traps arising from wind speed moderation by brush lines

Paired trap lines of five boil weevil pheromone traps each were placed on opposite sides of a brush line at six different sites on a plantation in the Lower Rio Grande Valley of Texas. Temperature, wind speed, and wind direction were monitored with a nearby weather station. We observed a strong negative relationship between mean daily wind speed and total daily capture of bell weevils. About half of the day-to-day variation in weevil captures was explained by wind speed alone. In addition, our data indicate that much of the variation between traps within days may arise from differences in local wind speed as governed by local vegetation depending on wind direction. Brush lines in this study slowed the wind by 40-70% and mitigated its effects such that traps on the leeward side averaged 2.5-2.9 times higher captures than traps on the windward side. The magnitude of the effect of windward or leeward placement of traps on weevil captures depended on the relative strength of the wind. Under light winds (<10 km/h), there were no increases in leeward trap captures. However, on days of moderate (10-20 km/h) or strong (>20 km/h) winds, leeward trap captures averaged 3.9- or 2.4 times greater than windward captures, respectively. By accounting for the ability of vegetation to dampen the effects of wind on boll weevil trap captures, we should be able to dampen daily and positional variation in trap captures by more careful placement of traps. Furthermore, judicious placement of traps in locations protected from prevailing winds should improve detection efficiency in areas where early warning of weevil presence is critical, such as in eradication and posteradication zones.