A seed midge pest of big bluestem

Abstract

A Cecidomyiid midge reared from the panicles of big bluestem (Andropogon gerardii Vitman (var. gerardii) at Mead, Neb., was identified as Contarinia wattsi Gagné. This midge was previously known only from panicles of little bluestem (Schizachyrium scoparium (Michx.) Nash) in New Mexico. In Nebraska, C. wattsi appears to have a minimum of 3 generations per season. Larvae of the earlier generations leave the florets after completing development, making it difficult to associate floret damage with the midge. Larvae of the last generation of a season remain in diapause, in the floret, throughout the winter. Evidence obtained in this study in 1985 indicates that, at harvest time, 7 and 15% of the florets in the 2 fields studied contained diapausing midges. However, when an estimate of seed loss by the earlier generations (as indicated by empty florets and small seed) was considered, the total loss was probably closer to 40%. An unidentified species of thrips (Thysanoptera: Thripidae) also was found in big bluestem florets during this study. However, evidence suggests that thrips do not damage big bluestem seed as seriously as the midge.