Feeding deterrent activity of terpenoid lactones with a p-menthane system against stored-product pests

Feeding deterrent activity of eight enantiomeric pairs and one optically inactive terpenoid lactone with a p-menthane system against three storage pests was determined. The lactones were tested on adults of Sitophilus granarius, adults and larvae of Tribolium confusum and larvae of Trogoderma granarium. The isomeric starting natural compounds, (+) and (−) pulegones and (+) and (−) isopulegols, were also tested. The results showed that the introduction of the lactone moiety into the p-menthane system produced antifeedant activity in the lactones obtained. The lactones with a spiro arrangement of lactone and cyclohexane rings were more active than those with condensed rings. The configuration of chiral centres present in the molecule significantly influenced the activity of the compounds studied. In most cases, lactones obtained from R-(+)-pulegone were more active antifeedants than those obtained from S-(−)-pulegone.