A Study of Anagrus Egg Parasitoids Important for Biological Control of Erythroneura Leafhopper Pests of Wine Grapes in California
In many of California wine grape vineyards, especially in San Joaquin and Sacramento Valleys, the variegated leafhopper (VLH) has become the dominant pest since it was first reported there in 1980, replacing the western grape leafhopper (GLH) in importance. While the two species of mymarid wasps of the genus Anagrus, previously known as A. epos, provided more or less satisfactory control of GLH before 1980, parasitism of VLH is lower and does not currently provide sufficient control. Cornerstones of biological control are the proper identification of natural enemy species as well as evaluation of their effectiveness in the field following release. From data we have collected, we believe that several Anagrus species that were imported to California and released in selected vineyards in San Joaquin Valley during 1986-1991 either have not established or perhaps interbred with the local populations. One of the species native to California, A. erythroneurae, is the most abundant natural enemy of both leafhopper species throughout California, whereas lesser numbers (ca 10-20%of all samples) of a yet undescribed species (A. sp. 1) have been recognized from collections made in the Napa, Sonoma, and San Joaquin Valleys. Overall, more than 5,000 specimens of Anagrus were examined and identified during our study including those reared from potential overwintering refuges, i.e., almond, apple, blackberry, prune and wild grape plants. The conclusions resulting from this two-year study and our recommendations for further research and biological control programs are presented.