Evaluation of soil-applied entomopathogens as biological control agents of the swede midge, Contarinia nasturtii

The swede midge, Contarinia nasturtii, is a serious pest of cruciferous vegetables, such as broccoli, cabbage and cauliflower, in North America.  Larvae feed on the growing point of the host plant, causing direct damage to the developing vegetable heads.  Although some control is achieved in conventional systems, organic growers have no effective management option, with some growers reporting losses of up to 100%.   The entomopathogenic nematodes Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae and the entomopathogenic fungus Metarhizium anisopliae are potential biological control agents targeting the soil-dwelling stages of the swede midge.  Laboratory bioassays were conducted to evaluate the infectivity of these entomopathogens on swede midge larvae and pupae across a range of temperatures commonly encountered in the field.  In larval assays, H. bacteriophora and S. feltiae yielded the highest mortality rates at 16ºC and H. bacteriophora was most effective at 25ºC.  The H. bacteriophora X M. anisopliae combination was the most effective treatment at 20ºC and 25ºC, suggesting a possible synergistic effect between these two entomopathogens.  In the pupal assays, H. bacteriophora was most effective at 16ºC and 25ºC, while S. feltiae was most effective at 20ºC.  The presence of H. bacteriophora enhanced the effectiveness of M. anisopliae across all temperatures.  Results from foliar applications of nematodes in greenhouse trials as well as field emergence trials conducted in 2013 at Elora, Ontario, Canada, will also be presented.