Potential of Entomopathogenic Nematodes to Control the Cabbage Stem Flea Beetle Psylliodes chrysocephala

SIMPLE SUMMARY: Cabbage stem flea beetles were controlled through the use of neonicotinoid insecticides to protect oilseed rape crops grown in the UK and other parts of Europe. However, since the ban of this class of insecticide for this use in 2013, the only authorized insecticides to control the cabbage stem flea beetle are pyrethroids, which are toxic to other insects and to which cabbage stem flea beetles have developed resistance. New control solutions are necessary, such as the use of entomopathogenic nematodes. Here we evaluated the potential of several entomopathogenic nematode species to control the adult cabbage stem flea beetle in the laboratory. Results are encouraging, with high flea beetle mortality obtained, i.e., 75% with Heterorhabditis bacteriophora, 80% with Steinernema feltiae, 85% with Steinernema carpocapsae and 70% with Steinernema kraussei as opposed to the control treatment which led to 23% mortality. Next, we tested whether entomopathogenic nematodes were compatible with different adjuvants that may protect nematodes against detrimental UV radiation and desiccation. All adjuvants tested were found to be compatible with nematodes under the laboratory conditions used. This study is a first step in developing an effective and safe solution to control the cabbage stem flea beetle in oilseed rape crops. ABSTRACT: Cabbage stem flea beetle (CSFB) is an important pest of oilseed rape that was controlled by neonicotinoid seed treatments until they were banned for this use in 2013. Since then, CSFB has been a difficult pest to control, partly due to widespread resistance to pyrethroid insecticides. Alternate solutions are necessary. Here, four entomopathogenic nematode (EPN) species were tested against CSFB adults under laboratory conditions. In addition, a bioassay was completed to test for EPN compatibility with a range of adjuvants (glycerin, xanthan gum and flame retardant) to protect EPNs from UV radiation and desiccation. Results show that EPNs have the potential to control CSFB adults under laboratory conditions. Heterorhabditis bacteriophora caused 75% CSFB mortality at a concentration of 4000 nematodes/mL after six days, Steinernema feltiae caused 80% CSFB mortality when applied at a concentration of 40,000 nematodes/mL after two days, Steinernema carpocapsae caused 85% mortality at a concentration of 10,000 nematodes/mL after six days, and Steinernema kraussei caused no more than 70% CSFB mortality overall compared to the water control, which led to 23% mortality. Steinernema feltiae and H. bacteriophora survival was 100% when exposed to adjuvants, except S. feltiae with glycerin and H. bacteriophora with flame retardant. Further research to evaluate the efficacy of EPN and adjuvants under field conditions is necessary.