Identification of Male Pecan Weevil Pheromone

Abstract

The pecan weevil, Curculio caryae is a serious economic pest of pecans (Caryae illinoensis). In late summer, the weevil attacks maturing nuts and damages them when making feeding and/or oviposition punctures. The larvae leave the nut and burrow into the soil, remaining there for two to three years before emerging as adults to commence another cycle. This present work has resulted in the identification of the male pecan weevil pheromone as a mixture of four components; I as both the cis and trans isomers of 2-propenyl-1-methyl-cyclobutaneethanol [also identified as (1R,2S)−(+ and −)-grandisol], II [(Z)-3,3-dimethylcyclohexane-Δ1,β-ethanol], III [(Z)-3,3-dimethylcyclohexane-Δ1,α-acetaldehyde], and IV [(E)-3,3-dimethylcyclohexane-Δ1,α-acetaldehyde]. They are synthesized by the male pecan weevil, but not by the female, in the ratio 7:16:3:3 of I, II, III, and IV, respectively. These same compounds were earlier identified as the pheromone of the male boll weevil, Anthonomus grandis (Boh.), in which they were isolated from frass in the ratio 6:6:1.5:1.5. However, only the (+) isomer of grandisol was synthesized by male boll weevil. In laboratory tests, 80% of female pecan weevils were attracted to a synthetic formulation based on the ratio found in male pecan weevils, while only 28% of the females were attracted to a synthetic formulation based on the ratio found in boll weevil frass. The attraction of males to these synthetic formulations was minimal (14, 4, and 2%, respectively). Live males and their extracts were also attractive to females, but males did not respond to male or females. Preliminary field tests demonstrated that females were attracted to males and the synthetic pecan weevil formulation, but not to the synthetic boll weevil formulation.