Effect of Mass Releases of Trichogramma pretiosum Against Lepidopterous Pests on Processing Tomatoes in Southern California, with Notes on Host Egg Population Trends1

Abstract

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 (Hubner), 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.