Ash Whitefly (Homoptera: Aleyrodidae) Overwintering and Biological Control by Encarsia inaron (Hymenoptera: Aphelinidae) in Northern California

Abstract

The ash whitefly, Siphoninus phillyreae (Haliday), was introduced into northern California in 1989–1990. It developed through two or more generations from fall through spring (overwinter) on toyon, Heteromeles arbutifolia Roemer, a native broadleaf evergreen shrub. In spring, whiteflies migrated to ash, Fraxinus velutina Torrey, and other deciduous hosts; whiteflies were absent or not detected on toyon during each of the three summers from 1990 to 1992. Ash whitefly densities were increasing before natural enemy introductions. About 98% of ash leaves were infested in 1991 (before establishment of introduced natural enemies) in comparison with <1% of leaves infested in 1992 (after natural enemy establishment).Whitefly densities declined by two to four orders of magnitude on both ash and toyon after the introduction and establishment of Encarsia inaron (Walker) (=partellopea) and Clitostethus arcuatus (Rossi) (Coleoptera: Coccinellidae). E. inaron is apparently the more important species. Unlike ash whitefly, which must migrate from deciduous hosts to overwinter on evergreen plants, E. inaron can survive the deciduous host–free period as adults or by slowly developing as immatures on fallen ash leaves, as well as by parasitizing whiteflies on evergreen plants. Biological control may be enhanced because overwintering parasiloids can already be present in the deciduous–host (ash) habitat when whiteflies migrate from toyon back to ash during the spring.

Siphoninus phillyreae, Encarsia inaron, biological control