Allium leafminer parasitoid (Halticoptera circulus)

Halticoptera circulus

(Hymenoptera: Pteromalidae)

The Allium leafminer (ALM) is native to Europe, however, it was first reported in the United States in Lancaster County, Pennsylvania in December 2005 (Barringer et al. 2018). Populations of allium leafminer constrain Allium spp. production by feeding and tunneling in marketable parts of allium plants, (Barringer et al. 2018, Nault et al. 2020). The primary damage of concern happens in the center of the plant where larvae feed and tunnel, causing pinholes that contaminate the plant and result in rejected, unmarketable leeks, onion, scallions, etc. This lack of marketable yield due to ALM damage has severe economic consequences for allium producers. Therefore, focus has been placed on integrated pest management programs to find effective insecticide chemistries, estimate correct timing of applications, use polycultural planting techniques, and implement biological control programs. Biological control programs in particular focus on identifying natural enemies such as Halticoptera circulus, that could be used to reduce populations (Lingbeek et al. 2021).

In Pennsylvania, ALM overwinter as pupae in the foliage of allium plants or in plant debris near the soil surface. In early spring, adults emerge as black colored true flies after an accumulation of 250 degree-days at a temperature threshold of 38°F. In Pennsylvania the emergence occurs around April 20, depending on the location. After emergence, adult ALM mate within 48 hours (Zinati et al. 2020). Female H. circulus are able to take advantage of this overwintering behavior by laying eggs in the body cavity of pupating ALM, where they develop and emerge in the spring (Lingbeek et al. 2021). The parasitoid wasp species is considered native and can be found throughout the United States. 

Despite its reduction of ALM and other Agromyzid species, and therefore reduction of damage to allium crops, populations of H. circulus are not sufficient as a standalone method for insect pest control. Halticoptera circulus adults are about 2 mm in length and can be recognized by their dark iridescent green body color and yellow antennae and legs. Females have a small, curved ovipositor. Males are slightly smaller in size than the females. Because populations of H. cireculus are already present in the United States, biological control programs should focus on supporting populations. Populations of H. circulus are not commercially available for release, therefore maximizing parasitism involves attracting and conserving this species. The presence of allium crops may be critical to attract populations of parasitoid wasps such as H. circulus. Although pesticide susceptibility studies have not yet been undertaken, it is likely that broad-spectrum insecticides will have negative effects on H. circulus populations, as well as herbicides that reduce floral and nectar availability which is often critical to H. circulus as well as many parasitoid wasp species survival. 

Learn More Section References

• Barringer, L.E., Fleischer, S.J., Roberts, D., Spichiger, S-E., Elkner, T. 2018. The first North American record of the allium leafminer. Journal of Integrated Pest Management 9(1) 8.
• Lingbeek, B., Roberts, D., Elkner, T., Gates, and M., Fleischer, S.J. 2021. Phenology, Development, and Parasitism of Allium Leafminer (Diptera: Agromyzidae), a recent invasive species in the United States. Environmental Entomology 50(4): 878-887.
• Nault, B. A., L. E. Iglesias, R. S. Harding, E. A. Grundberg, T. Rusinek, T. Elkner, B. Lingbeek, and S. J. Fleischer. 2020. Managing allium leafminer (Diptera: Agromyzidae): An emerging pest of allium crops in North America. Journal of Economic Entomology 113: 2300-2309.
• Zinati, G.M., T. Valentine, J. Lang, and D. Kemper. 2020. Allium leafminer: A new culprit targeting allium crops in Pennsylvania and neighboring states. Rodale Institute, Kutztown, PA. 2 pages.