Discovery of Anagyrus schoenherri (Westwood, 1837) (Hymenoptera: Encyrtidae) in the Nearctic Region, a parasitoid of the apple mealybug Phenacoccus aceris (Signoret, 1875) (Hemiptera: Pseudococcidae) in Washington, U.S.A., with notes on the host.
Phenacoccus aceris (Signoret, 1875), the apple mealybug, is a vector of little cherry virus 2 (LChV2), a causal pathogen of little cherry disease. Sweet cherry (Prunus avium Linnaeus) (Rosaceae) trees infected with LChV2 produce cherries of small size, poor color, and poor flavor, making the fruit unmarketable. Little cherry disease was first observed in British Columbia, Canada in 1933, where it had a dramatic impact on sweet cherry production, and was recently detected in Washington, U.S.A. cherry orchards. In 2014-2016, a natural infestation of P. aceris was monitored in an apple orchard located in Washington State University's Sunrise Orchard near Rock Island, Washington (47°18′45.14″N 120°04′08.31″W). Heavy parasitism was observed on overwintering nymphs and ovipositing female P. aceris, followed by a reduction in P. aceris crawlers. The emerged wasps were identified as the encyrtid Anagyrus schoenherri (Westwood, 1837). This is the first report of A. schoenherri parasitizing P. aceris in a Washington apple orchard, which represents an extension of the geographic distribution of A. schoenherri to the Nearctic Region. Reduction in P. aceris densities, one of the key vectors of LChV2, is potentially important for the sweet cherry industry in the Pacific Northwest. Historically, declining P. aceris populations in British Columbia were attributed to the establishment of a platygastrid parasitoid Allotropa utilis Muesebeck, 1939, suggesting that biological control could play a major role.