Bluestem Gall Midge Annual Production Cycle and Effects on Grass Seed Production

Thebluestem gall midge (Stenodiplosiswattsii Gagne)is native to the grasslands of North America. It feeds on the developing seedsof warm-season grasses during a portion of its lifecycle, but little is knownof the biology and extent of gall midge infestations in native warm-seasongrasses in the USA. We investigated the infestations of the bluestem gall midgein big bluestem (Andropogon gerardii Vitman), sand bluestem (Andropogon gerardii var paucipilus), little bluestem [Schizachyriumscoparium (Michx.) Nash], and indiangrass [Sorghastrum nutans (L.)Nash] commercial seed production fields during 2001 through 2004. Ourobjectives were to determine the annual production cycle of the bluestem gallmidge, the range of the infestation in Nebraska, and estimate its impact onseed production. In eastern Nebraska, the midge goes through four generationswith the fourth entering a larval diapause, overwintering in seeds and emergingin mid-June of the following year. The bluestem gall midge damaged from 31% ofthe little bluestem seed to 67% of the big bluestem seed, and, on average,reduced the production of viable seed by 54% across the four grass species ineastern Nebraska. Additionally, the warm-season prairie grasses were surveyedin nine other counties in Nebraska and the bluestem gall midge was found ineach species surveyed from all nine counties. This study is the first todocument the negative effects of the bluestem gall midge on the production ofviable seed in sand bluestem and indiangrass.