Onion Maggot, Delia antiqua (Meigen) (Diptera: Anthomyiidae)

Onion maggot (onion fly) is now found throughout the northern hemisphere. It apparently was introduced to North America from Europe soon after European colonists arrived, in the 1600s or 1700s, and was recognized as a serious pest in North America by the early 1800s. It is favored by cool weather, and is a serious pest only in northern areas.

Life History

The number of generations is two or three per year, with a proportion of each generation diapausing as puparia until the next year. At the latitude of Quebec, Canada, adults from overwintering insects appear in May and initiate the first generation, with peak emergence of the first generation occurring in early July. The second generation begins emerging in mid to late August, with peak emergence about the first of September. Third generation insects all enter diapause, forming the overwintering population that emerges the following spring. The proportion of insects entering diapause in the first and second generations is reported to...