Olfactory preferences of the allium leafminer, an emerging pest in North America: comparison of three experimental bioassays.

Evaluating the olfactory preferences of emerging insect pests is critical to develop monitoring tools and improve early detection and management strategies. Here the chemical ecology and olfactory preferences of the allium leafminer Phytomyza gymnostoma Loew (Diptera: Agromyzidae), an invasive pest in North America affecting allium crops such as leeks and onions, were investigated. Three bioassay methods were assessed under laboratory conditions: wind tunnel, Y-tube olfactometer, and arena bioassay. All bioassays measured the responses of P. gymnostoma adults to odors of host and non-host plants. Two common allium crops, leek and chive, were used as host plants. Results of the wind tunnel bioassays showed a clear preference for host plants compared to non-host plants, with leek being twice as attractive as chive. Leek plants already infested by P. gymnostoma were half as attractive as healthy plants. Olfactometer and arena bioassays failed to show any significant response of adult flies toward host plant volatiles. This study is the first to compare multiple bioassays for behavioral investigations of P. gymnostoma, providing novel insights into the pest's host-finding behavior and highlighting methodological considerations for future work. Overall, these results suggest that both visual and chemical cues play a role in P. gymnostoma's foraging behavior and are a promising first step toward the development of monitoring tools against this invasive pest.