Influence of a Cysteine Proteinase Inhibitor on Alfalfa Weevil (Coleoptera: Curculionidae) Growth and Development Over Successive Generations

The influence of leupeptin, a cysteine and serine proteinase inhibitor, on alfalfa weevil, Hypera postica (Gyllenhal), growth and development was investigated over nine successive generations. Concern that ingestion of proteinase inhibitors by phytophagous insects could induce production of inhibitor-insensitive proteinase activity initiated this investigation. The percent alfalfa weevil larval, pupal and adult survival, and defoliation was significantly lower on alfalfa foliage treated with leupeptin than on untreated foliage in all nine generations tested. Main effects for generations and treatment times generation were nonsignificant for all variables. This study demonstrates that after nine generations leupeptin, when compared to an untreated control, does not lose its ability to significantly inhibit alfalfa weevil growth and development. This suggests that the alfalfa weevil did not utilize or induce other proteinases (digestive enzymes) to compensate for inhibition of one of its major proteinases.