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Allium leafminer, Phytomyza gymnostoma (Diptera: Agromyzidae), is an invasive species first recorded in the Western Hemisphere in 2015 and has expanded its range into northeastern and MidAtlantic states. Its host range encompasses Allium species grown for food and ornamentals, weedy species, species used for pollinator provisioning, and species of conservation concern. Using field and laboratory studies, we advanced methods for rearing, developed a phenology model for spring emergence, describe pupal development, and report on parasitism. Spring emergence was best detected by scouting wild alliums as opposed to emergence cages, and modeled using 350 degree-days above a lower threshold of 1.0°C. Spring adult flight occurred for about 5 wk. Larval development required 22 and 20 d at 17.5 and 25°C, respectively. Pupal development progressed along a color gradient, and an initial presence of fat cell clusters and an air bubble, followed by an exarate pupa. Pupal developed at 3–5% per day at 30°C and reached 25% per day at 21.5°C, but development was not successful at 30°C. Although parasitism rates were low, we documented two Chalcidoidea parasitoids, Halticoptera circulus (Walker) (Hymenoptera: Pteromalidae) and Chrysocharis oscinidis Ashmead (Hymenoptera: Pteromalidae). Together, these data provide baseline information to advance IPM for this invasive species both in crops and noncrop areas.

Allium leafminer, Phytomyza gymnostoma Loew, is the newest invasive pest of allium crops in North America. Larvae initially feed in the upper canopy before mining toward the base of the plant to pupate. Crop loss occurs when larvae destroy vascular tissue, facilitating infection by bacterial and fungal pathogens that cause rot. Contamination also occurs when larvae and pupae are present at harvest. In response to this invasion, efficacy of 14 insecticide active ingredients applied via foliar sprays, transplant treatments, and drip chemigation was evaluated for managing P. gymnostoma. Multiple field studies were conducted in onions, leeks, and scallions in Pennsylvania and New York, United States in 2018 and 2019. The highest and most consistent levels of P. gymnostoma control occurred using foliar applications of dinotefuran, cyantraniliprole and spinetoram (84–89% reduction in damage; 95% reduction in P. gymnostoma densities). Despite the success of dinotefuran and cyantraniliprole applied as foliar sprays, neither was effective in controlling P. gymnostoma when administered via drip chemigation. Other foliar-applied insecticides that significantly reduced densities of P. gymnostoma in one or two experiments included abamectin, acetamiprid, cyromazine, imidacloprid, lambda-cyhalothrin, methomyl, and spinosad. Active ingredients that never controlled P. gymnostoma included azadirachtin, kaolin clay, pyrethrin, and spirotetramat. Spinosad applied to bare-root and plug-tray transplants immediately before transplanting reduced P. gymnostoma damage in the field by >90%. Implications of using these insecticides and application strategies are discussed within the context of developing a sustainable IPM program.

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