Augmentation of Euseius tularensis (Acari: Phytoseiidae) in Citrus

Abstract

Single releases of the predacious mite, Euseius tularensis Congdon, and additions of apple pollen were made in the spring of 1991 in three citrus orchards in the San Joaquin Valley of California. Dusting citrus trees with apple pollen had no significant effect on the predacious mite populations at this time of year. In two of the three orchards, releases of 500 or 2,000 E. tularensis per tree significantly increased the cumulative number of predacious mites found in the trees before or during the period of fruit susceptibility to citrus thrips. In 1992, single releases of 2,000 mites and four releases of 100 or 500 predacious mites were compared with nonrelease trees in two orchards. One site had relatively high natural densities of predacious mites and was not significantly affected by predacious mite releases. In the other site, the peak density of E. tularensis was improved 2-fold by releases of E. tularensis. A single release of 2,000 E. tularensis per tree was more beneficial than multiple releases of 500 or 100 mites. A greater cumulative number of predacious mites was significantly correlated with improved biological control of citrus thrips, Scirtothrips citri (Moulton), as measured by reduced heavy scarring of fruit in the 1992 orchards. This suggests that E. tularensis can be important in reducing citrus thrips in citrus groves managed under a selective pesticide program.