The orange wheat blossom midge, S. mosellana (Gehin) (Diptera: Cecidomyiidae), a global pest of wheat (Tritium aestivum L.), has recently invaded Montana's Golden Triangle, an important wheat producing region. Unchecked, S. mosellana populations can quickly grow to damaging levels. In this study, we document the prevalence of S. mosellana and its main natural enemy, Macroglenes penetrans (Hymenoptera: Pteromalidae), in this newly invaded area of Montana, and compared the effects of irrigated versus dryland cropping systems on S. mosellana and its parasitoid. Different approaches to monitoring S. mosellana populations were examined, including pheromone traps for adults, collection of larvae from wheat heads, and overwinter sampling of soil to measure the levels of larvae and cocoons. Adults of the M. penetrans were surveyed through daily sweep net sampling. This study demonstrated that the emergence of M. penetrans was usually well synchronized with emergence of S. mosellana as the emergence of parasitoids occurred shortly after the pest with the highest peak (90%) at 26 June and 14 July, 2015, respectively. Irrespective of sampling techniques; pheromone traps or soil sampling, no significant difference was observed in population of S. mosellana between irrigated and dryland cropping systems. In contrary, cropping systems played a significant role in the abundance of parasitoids since the irrigated fields had significantly higher population of parasitoids (five times on an average) compared to dryland cropping system. The possible implications of these findings in monitoring of S. mosellane and the establishment of M. penetrans are discussed.
