Effect of Mass Releases of Trichogramma pretiosum Against Lepidopterous Pests on Processing Tomatoes in Southern California, with Notes on Host Egg Population Trends

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Mass releases of Trichogramma pretiosum Riley in processing tomatoes at rates equivalent to 200,000 to 318,000/0.4 ha in 1970 through 1974 resulted in an average parasitization of eggs of the tomato fruitworm, Heliothis zea (Boddie), ranging from 53.1 to 85.4% in the release fields, compared to 0 to 41.4% in the nonrelease fields. Average parasitization of eggs of the cabbage looper, Trichoplusia ni (Hübner), and Manduca spp. ranged from ca. 3 to 47% and 18 to 68% higher, respectively, in the release fields than in the nonrelease fields. When harvested by mid-August, fruit injured by H. zea was considerably less in the release field (0.9%) than in the nonrelease field (5.4%). There was little difference in fruit injury between fields when the fruit was harvested in late August. Mean population trends of H. zea, T. ni, and Manduca spp. eggs, during a 5-year period (1968–72), showed 4 peak oviposition periods for each species between May and September. The highest egg population of H. zea occurred in June and that of the other 2 species in late August or early September.

Document Type: Research Article

Publication date: December 1, 1978

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