Host plant and other volatiles for attraction of carrot weevil, Listronotus oregonensis

The carrot weevil is a pest insect that causes considerable damage to various Apiaceae crops, such as carrot, parsley, celery and celeriac. To control its population, an integrated pest-management program relies on the use of baited traps to identify fields with high abundance requiring insecticide applications. Recently, a second generation of weevils in Quebec, Canada, has been observed and these are not as attracted to these baited traps as the emerging generation. The objectives of our study were to evaluate host plant preferences for oviposition and their attractiveness for carrot weevil adults in order to improve trapping efficiency in the field. To do this, oviposition rates on host plants were compared in a greenhouse experiment, and two-choice tests were conducted using essential oils from the four most-preferred host plants for egg laying. Females laid between 2.0 and 15.4 eggs/plant over a four-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 equally attractive when used alone. However, in the presence of fresh carrots, the attractiveness of these essential oils decreases considerably, and only the caraway essential oil showed a significant attraction. Improvement of monitoring techniques targeting the second generation of carrot weevils should rely on diverse IPM strategies such as the use of other semiochemicals (sexual and aggregation pheromones) and predictive models based on first generation trap captures.