AUGMENTATION OF EUSEIUS-TULARENSIS (ACARI, PHYTOSEIIDAE) IN CITRUS

Single releases of the predacious mite, Euseius tularensis Congdon, an d additions of apple pollen were made in the spring of 1991 in three c itrus orchards in the San Joaquin Valley of California. Dusting citrus trees with apple pollen had no significant effect on the predacious m ite populations at this time of year. In two of the three orchards, re leases 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 predaci ous mites were compared with nonrelease trees in two orchards. One sit e had relatively high natural densities of predacious mites and was no t significantly affected by predacious mite releases. In the other sit e, the peak density of E. tularensis was improved 2-fold by releases o f 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 wit h improved biological control of citrus thrips, Scirtothrips citri (Mo ulton), as measured by reduced heavy scarring of fruit in the 1992 orc hards. This suggests that E. tularensis can be important in reducing c itrus thrips in citrus groves managed under a selective pesticide prog ram.