Behavioral Responses of Plum Curculio (Coleoptera: Curculionidae) to Different Enantiomer Concentrations and Blends of the Synthetic Aggregation Pheromone Grandisoic Acid.

The plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), is an important pest of fruit in North America. Males produce an aggregation pheromone (grandisoic acid) that attracts both sexes of the northern univoltine and the southern multivoltine strains. Grandisoic acid ((1R,2S)-1-methyl-2-(1-methylethenyl)-cyclobutaneacetic acid) is a chiral molecule containing one chiral center. A synthetic racemic mixture will contain two optical isomers that are mirror images of each other with equal amounts of (+)- and (-)-enantiomeric isomers. Male plum curculio only produce the (+) enantiomer. Some enantiomers can have antagonistic effects on the attraction of weevils to pheromones. An understanding of the effect of both enantiomers on the behaviour of plum curculio is needed to develop more efficient trap baits. Behavioural bioassays were conducted in a dual-choice still-air vertical olfactometer using a quantity of 1.5 ml of both (+) and (-) synthetic enantiomers and the racemic mixture of grandisoic acid with live female responders to determine which concentration and enantiomeric purity is the most attractive and if there is an antagonistic effect of the unnatural (-) enantiomer. Results indicated that plum curculio were attracted to low concentrations of the (+) enantiomer at 72% enantiomeric excess, but that strains were attracted to different concentrations of the (+) enantiomer (2×10(-7) mg/ml for univoltine, 2×10(-9) mg/ml for multivoltine).

Evaluating electrophysiological and behavioral responses to volatiles for improvement of odor-baited trap tree management of Conotrachelus nenuphar (Coleoptera: Curculionidae).

Plum curculio, Conotrachelus nenuphar (Herbst), one of the most important pests of apple in eastern and central North America, is usually managed in New England apple orchards by multiple full-block insecticide applications. Efforts to reduce insecticide inputs against plum curculio include using an "attract and kill" approach: odor-baited trap trees deployed in the perimeter row of apple orchards. The standard approach is based on baiting apple trees with two olfactory stimuli, the fruit volatile benzaldehyde and the aggregation pheromone of plum curculio, grandisoic acid. We attempted to improve attraction, aggregation, and retention of adult plum curculios within specific baited trap tree canopies within apple orchards using an additional host plant volatile found to be highly stimulating in electroantennogram studies, trans-2-hexenal. We also attempted to increase aggregation using increased release rates of grandisoic acid. We found that trans-2-hexenal did not provide increased aggregation when deployed as an additional attractant within trap trees or when conversely deployed as a "push" component or repellent in perimeter trees lateral to the baited trap tree. Although increasing the release rate of grandisoic acid 5× actually appeared to increase overall aggregation within trap trees, it was not significantly different than that obtained using the standard dose. Therefore, we believe that the standard olfactory stimuli are sufficient to provide aggregation within trap trees, but that other means should be used to manage them after their arrival.