Mechanisms of boll weevil (Coleoptera : Curculionidae) bait stick activityrelative to pheromone traps

Mechanisms of bait stick activity against boil weevil, Anthonomus grandis g randis Boheman, including attractiveness relative to traps, competition wit h traps, longevity of the pheromone lure, and behavior and mortality of res ponding weevils, were studied in the Lower Rio Grande and Brazos Valleys of Texas. Adhesive-coated bait sticks captured 2-4 times as many weevils as a dhesive-coated trap bases, although the lateral surface area of the bait st ick was only 1.5-fold that of the trap base. Overall, reductions in trap ca ptures because of competitive interactions with bait sticks were not clearl y demonstrated. However, temporal patterns of capture suggested that compet ition from bait sticks may have reduced trap captures initially when bait s tick pheromone sources were fresh. Initial pheromone release rates by the b ait stick lure were approximate to 8.1 times greater than for the trap lure and may have caused a temporary competitive effect. Responding weevils did not feed on or probe the bait stick surface, and when stationary assumed a departure posture with the tip of the abdomen held low and the head held h igh. Responding weevils contacted the bait stick for an average of 9.4 +/- 1.7 min, but nearly half remained on the device for <5 min. Exposure to the bait stick in the field resulted in mortality similar to that of unexposed weevils, whereas forced-contact bioassays indicated high levels of mortali ty. These results indicate that forced-contact bioassays may be inappropria te for assessing the toxicity of the bait stick to boil weevils.