Monogenic reproduction of the soybean gall midge (Resseliella maxima Gagné)

Sex determination in gall midges is complex and remains poorly understood; the precise mechanisms and evolutionary origins remain elusive. Several species within Cecidomyiidae and the closely related dipteran families have reported monogenic reproductive strategies, wherein genotypically distinct mothers are genetically predetermined to produce exclusively or predominantly single-sex offspring. Soybean gall midge (SGM), Resseliella maxima Gagné (Diptera: Cecidomyiidae), is a newly described species that has been found infesting soybean in the United States. As of 2025, SGM has been found infesting soybean within seven U.S. states: Iowa, Kansas, Minnesota, Missouri, Nebraska, and South Dakota where yield reductions of up to 31% in field interiors, and near total losses around field edges have been attributed to SGM infestations. In this study, individual soybean plants were caged and infested with a single mated SGM female. The resulting progeny recovered from the plant stem were reared to adulthood, and the sex and emergence phenology of emerging adults were recorded. Of the attempted replicates, successful oviposition occurred with 40 females resulting in 22 exclusively female broods, 16 exclusively male broods, and 2 mixed sex broods. Protandry, the early emergence of males, which is especially common in monandrous species, was also documented. An understanding of the factors that influence sex ratio in SGM may be a useful tool in developing effective integrated pest management strategies such as the use of pheromone traps, determining the timing of treatments, or the role of resistant crops.