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

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, estimates of the pheromone emitted by weevils fed bolls are not available. We used headspace collections to determine (1) whether male weevils already emitting pheromone could sustain production on bolls, and (2) whether pheromone emission could be initiated on a boll diet. Male weevils switched to a diet of small (12 - 15 mm diam) or medium (20 - 23 mm diam) sized bolls after feeding on squares (5 - 7 mm diam) for 7 d maintained pheromone releases at levels >= that of weevils remaining on squares through the 13(th) day of adulthood. Pheromone composition did not vary substantially among the diets. When the diets were provided beginning at adult eclosion, weevils initiated pheromone emission similarly on all diets, but weevils fed small bolls released 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. Our findings also 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.