Grass-feeding gall midges (Diptera: Cecidomyiidae) and their parasitoids in Eastern South Dakota

Native and introduced grass species, excluding grain crops, remain dominant components of the vegetational landscapes of the northern Great Plains. Many of the characteristic and conspicuous grass species have host specific gall midges (Diptera: Cecidomyiidae). However there are few published studies on these flies in the region, their host associations, or their parasitoids. Grass feeding gall midges investigated feed on inflorescence structures and immature caryopses, thus decrease the reproductive success of their hosts. Native gall midges, i.e. Chilophaga virgati Gagné, Stenodiplosis wattsi Gagné and Stenodiplosis n.sp., have demonstrated impacts as pests on grasses grown for seed and cellulosic ethanol. The introduced S. bromicola Marikovskiy & Agafonova and S. geniculati Reuter reduce seed production and may provide previously unrecognized biological control activity on their invasive host grasses. Adult gall midges and parasitoids were field collected on host plants. Inflorescences and florets were sampled during 2014 and 2015, and adult gall midges and parasitoids reared for identification, confirmation of host associations, and life history compilations. Gall midges found in dominant native and introduced grasses in eastern South Dakota belong to the genera Chilophaga, Dasineura, and Stenodiplosis, and each has multivoltine populations influenced by seasonal conditions. Gall midge species-specific intraguild competition by parasitoids was found, revealing endo- and ectoparasitoids affecting population dynamics and their impact on economic value. The introduced parasitoid Aprostocetus bromi (Hymenoptera: Eulophidae) was found to co-parasitize larvae of both native and introduced gall midges with apparently undescribed native congeneric species.