Fate of the cereal leaf beetle egg parasitoid, Anaphes flavipes, in Washington state

Cereal leaf beetle (CLB, Oulema melanopus), an invasive pest of cereal grains, was detected in the arid grain-growing region of eastern Washington State, USA, in 1999. In 2001 we began releases of the CLB egg parasitoid Anaphes flavipes, in an attempt to reproduce the successful biological control this parasitoid exerts in eastern North America. Despite the release of thousands of adult wasps over 5 years, percent parasitism of CLB eggs are our release sites remains < 0.1%. In a complementary laboratory experiment we found that longevity of adult A. flavipes was dramatically reduced under the low humidity conditions (25% relative humidity) typical of our region. Provisioning A. flavipes adults with access to either honey or a sprig of sweet alyssum (Lobularia maritima) flowers increased the lifespan of adult wasps, but average longevity remained < 24 h at low humidity. In a subsequent laboratory experiment we found that exposure to a pyrethroid insecticide (lambda-cyhalothrin) commonly used in regional grain production was toxic to A. flavipes. However, two selective aphicides, pymetrozine and flomicamid, were significantly less harmful to adult wasps. Thus, both provisioning of floral resources and a switch to selective insecticides have the potential to encourage A. flavipes survival in the field. Nonetheless, the sensitivity of A. flavipes to dry conditions, along with a regional paucity of alternative overwintering hosts, likely form insurmountable obstacles to our successful use of this wasp as a CLB biocontrol agent..