Classical biological control of the western grape leaf skeletonizer in California, a review 1941–2022

Abstract

ABSTRACT Western grape leaf skeletonizer was first reported in southern California in 1941 and soon became a serious pest of commercially produced grapes in that region. Their gregarious larvae can easily defoliate vineyards and they remained a major problem for production of grapes until this pest was reunited with its host-specific natural enemies. Efforts to import into southern California effective natural enemies during the 1950s from southern Arizona succeeded in reducing populations of this moth to economically tolerable levels. We report for the first time on releases of natural enemies into central and northern California for control of western grape leaf skeletonizer. Over 600,000 parasitoids new to this region were released during late 1970s–1980s by the state’s Biological Control Program. Foreign exploration by the California Department of Food and Agriculture (CDFA) into Mexico in 1978 resulted in additional parasitoids new to California: a new biotype of Ametadoria harrisinae and a new species of Chetogena sp. (Tachinidae). The high numbers of tachinids released throughout California is credited with aiding in the spread of a highly virulent strain of granulosis virus which in turn caused high levels of mortality to western grape leaf skeletonizer larvae. Reports of WGLS outbreaks in vineyards over the last 15 years are rare, in contrast to previous years.