EVALUATING THE EFFECTIVENESS OF ANTS AS BIOLOGICAL-CONTROL AGENTS OF PEAR PSYLLA (HOMOPTERA, PSYLLIDAE)

Ant exclusion barriers were constructed in two Chelan County, Wash., pear orchards to prevent ants from foraging in pear tree canopies. Orchard 1 had a naturally occurring high density of Formica neoclara (Emery), a predatory ant. Ants were introduced into Orchard 2 in August 1987. Exclusion studies were carried out in Orchard 1 during 1987-1989 and in Orchard 2 during 1988-1989. Each year, adult and immature pear psylla population densities in selected trees were estimated by beating tray and leaf sampling. During most years, adult and immature pear psylla, Cacopsylla pyricola (Foerster), population densities were significantly higher in ant-excluded trees. In Orchard 2, densities of immature psylla were significantly higher before ant introduction than after introduction on trees without exclusion barriers. Psylla densities did not differ from postant introduction densities in ant-excluded trees. This study showed that predatory ants can significantly reduce pear psylla population densities.