Submitted to: Journal of Entomological Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/16/2013
Publication Date: 4/14/2014
Citation: Suh, C.P., Westbrook, J.K. 2014. Failure of pheromone traps in detecting incipient populations of boll weevils (Coleoptera: Curculionidae): Investigation of two potential contributing factors. Journal of Entomological Science. 49(2):211-214. Interpretive Summary: Eradication of the boll weevil has been delayed in the southern areas of Texas due the inconsistent performance of pheromone traps in detecting weevil populations. Because eradication programs rely exclusively on captures of weevils in traps to indicate the need for insecticide treatments, factors responsible for these detection failures must be identified and resolved. We investigated boll weevil pheromone production and examined the quality of commercial pheromone lures used in a cotton production area experiencing delayed progress towards eradication. We found no evidence of resident boll weevils producing a unique blend of pheromone. However, lures in half of the sampled packages were relatively small and, subsequently, did not contain the standard amount of pheromone. Consequently, these lures may not have released enough pheromone to attract weevils to traps throughout the two-week lure replacement interval. Eradication program success would be facilitated by a specific standard of lure quality from manufacturers, by routine monitoring of the pheromone content of lures, and by reducing the replacement interval of lures in areas where weevil detection has been problematic.
Technical Abstract: Progress towards complete eradication of the boll weevil has been delayed in some areas of Texas due to the inconsistent performance of pheromone traps in detecting incipient weevil populations. In 2008 substantial infestations of boll weevils, Anthonomus grandis Boheman, were detected in several cotton, Gossypium hirsutum L., fields in Medina Co., TX, but adjacent traps failed to capture weevils during the preceding weeks. We examined the composition of pheromone produced by boll weevils in Medina Co., TX to determine whether resident weevils produce a unique blend of pheromone and subsequently, no longer respond to the standard grandlure formulation. We also examined the pheromone content of lures from packages leftover from the 2008 trapping season in Medina Co. The mean ratio of the four pheromone components produced by field-collected (44:43:2:11) and trap-captured (43:43:3:11) boll weevils were essentially the same, and both ratios were nearly identical to the ratio (45:42:3:10) previously reported for weevils collected from other areas of Texas. Thus, we found no evidence of weevils in Medina Co. producing a unique pheromone blend. Although each lure package was supposed to contain lures dosed with 10 mg of grandlure, the average pheromone content of lures varied significantly among packages, ranging from 7.1 mg in one package to 12.0 mg in another package. We found a strong relationship (r2=0.71) between the grandlure content and weight of lures. Thus, the variation in pheromone content among lures from different packages appeared to be simply related to the manner in which the manufacturer cut and packaged the lures, and not because grandlure was unevenly distributed among lures. It is possible that the use of lures containing a sub-standard amount of grandlure may not have released enough pheromone to attract weevils to traps for the entire two week lure replacement interval. In light of our findings, eradication program success may be facilitated by a specific standard of lure quality from manufacturers, by routine monitoring of the pheromone content of lures, and by reducing the replacement interval of lures in areas where weevil detection has been problematic.