Response of carrot weevil (Listronotus oregonensis) to different host-plant essential oils

Abstract

The carrot weevil is an insect pest that causes considerable damage to Apiaceae crops. To control its population, an integrated pest-management (IPM) program relies on the use of carrot-baited traps to identify fields requiring insecticide application. Recently, an additional generation of weevils has been observed in Canada and these newly emerged adults are not as attracted to traps as the overwintering generation since there is competition with carrots growing in the field. The main objective of our study was to identify host-plant essential oils with potential to attract carrot weevil adults and improve trapping efficiency in the field throughout the growing season. To do this, oviposition rates on six different host plants were compared in a greenhouse experiment, with two-choice tests conducted using essential oils of the four most preferred host plants. Females laid between 2.0 and 15.4 eggs/plant over a 4-day period, and only parsley and parsnip plants had significantly fewer eggs compared to carrot, dill, celery and caraway plants. Two-choice tests validated that essential oils from Apiaceae plants are all attractive when tested alone. However, in the presence of fresh carrots, the attractiveness of these essential oils decreased, with only caraway showing significant attraction. Finally, in the field, no increase in carrot weevil catch was recorded using caraway essential oil compared to regular baited traps using fresh carrots. Improvement of monitoring techniques targeting the newly emerged adults of carrot weevils should rely on other IPM strategies, such as the use of other semiochemicals and predictive models based upon catches of the first generation.