Efficiency of natural enemies against the swede midge Contarinia nasturtii (Diptera: Cecidomyiidae), a new invasive species in North America

The swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae), a widespread pest of cruciferous crops in Europe, has been recently found in Canada. A 2-year survey in Quebec yielded no specialized natural enemies. Two polyphagous coccinellid predators (Harmonia axyridis (Pallas) and Coccinella septempunctata L) were field collected for further evaluation. In laboratory experiments, these two coccinellid species fed on swede midge larvae, and H. axyridis showed a higher voracity than C. septempunctata. Late larvae and adults of H. axyridis were shown to consume more swede midge larvae than young larvae, while the adults of H. axyridis showed no preference between swede midge larvae and the green peach aphid Myzus persicae. However, H. axyridis adults were not able to prey on swede midge larvae on potted infested broccoli plants. The susceptibility of swede midge larvae to three species of entomopathogenic nematodes (Steinernema feltiae, Steinernema carpocapsae, and Heterorhabditis bacteriophora) was also evaluated. H. bacteriophora was the only species that caused significant mortality to swede midge larvae. At a concentration of 1000 IJs/larva, H. bacteriophora caused 90–100% mortality to swede midge larvae in loam, sandy loam, clay and muck soils.