Pheromone Production by the Boll Weevil (Coleoptera: Curculionidae) Fed Cotton Squares and Bolls.

Authors: Spurgeon, Dale; Suh, Charles

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2008
Publication Date: 8/11/2009
Citation: Spurgeon, D.W. and C.P.-C. Suh. 2009. Pheromone Production by the Boll Weevil (Coleoptera: Curculionidae) Fed Cotton Squares and Bolls. Journal of Entomological Science. 44:209-221.

Interpretive Summary: The male boll weevil communicates with other boll weevils by producing a specific mixture of chemicals (pheromone). While pheromone is produced on a variety of diets, access to flower buds (squares) or small fruit (bolls) of cotton is thought necessary for high levels of pheromone production. However, pheromone production by weevils fed bolls has not been examined in detail. In laboratory studies we found that square-fed male weevils already producing pheromone continued to produce pheromone at high levels when they were fed bolls. When male weevils were initially fed either squares or bolls, those fed small bolls (about 1/2 inch diameter) produced more pheromone by the ninth day than those fed squares or larger bolls. In all experiments, weevils exhibiting the characters of dormancy associated with overwintering produced little or no pheromone. However, for those that did not enter dormancy, the mixture of chemicals composing the pheromone was similar regardless of the type of food. The high levels of pheromone production by weevils fed bolls may provide a mechanism to ensure that late-season females destined to overwinter are mated before they leave maturing cotton. Our results also suggest reduced pheromone production by weevils in maturing cotton is not an adequate explanation for the commonly observed late-season increases in weevil captures by pheromone-baited traps. This information should be useful to action programs that rely on pheromone-baited traps for monitoring boll weevil population levels.

Technical Abstract: The boll weevil, Anthonomus grandis Boheman, produces pheromone on a variety of diets, but access to flower buds (squares) or small fruit (bolls) of cotton, Gossypium hirsutum L., is thought necessary for high levels of pheromone production. However, quantitative estimates of pheromone production by weevils fed bolls are not available. We used headspace collections to determine 1) whether male weevils already producing pheromone could sustain production on bolls, and 2) whether pheromone production could be initiated on a boll diet. Male weevils switched to a diet of small (12-15 mm diameter) or medium (20-23 mm diameter) sized bolls after feeding on squares (5-7 mm diameter) for 7 d maintained pheromone production at levels >/= that of weevils remaining on squares through the 13th day of adulthood. Pheromone composition did not vary substantially among the diets. When the diets were provided beginning at adult eclosion, weevils initiated pheromone production similarly on all diets, but weevils fed small bolls produced the most pheromone by day 9 of adulthood. No difference in pheromone composition was observed among the diet treatments. In addition, weevils that entered diapause by the end of the experiments produced only small amounts of pheromone. The high levels of pheromone production by weevils fed bolls may be ecologically important in ensuring that potential overwintering females are mated before emigrating from maturing cotton, and suggest that diminished competition between naturally-produced pheromone and traps is not an adequate explanation for commonly observed increases in late-season captures by pheromone traps.