Biological Control of the Tomato Fruitworm, Cabbage Looper, and Hornworms on Processing Tomatoes in Southern California, Using Mass Releases of Trichogramma pretiosum123

Abstract

Parasitization of eggs of the tomato fruitworm, Heliothis zea (Boddie), the cabbage looper, Trichopilusia ni (Hübner), and horn worms (primarily the tobacco hornworm, Manduca sexta (Johannson)), was studied on tomato foliage in Orange County, Calif., in 1966 and 1967. Mass releases of Trichogramma for biological control of these pests on processing tomatoes were assessed, using a uniparental species in 1968 and the native T. pretiosum Riley in 1969. Parasitization of tomato fruit worm, cabbage looper, and horn worm eggs averaged 55.7, 53.4, and 49.5%, respectively, for the June-August survey period in 1966 and 51.4, 24.6, and 41.9% for the August-October period in 1967. T. pretiosum was the only parasite reared from the eggs. In 1966 and 1967, 12.7 and 11.9%, respectively, of the tomatoes were in of the jured by the tomato fruit worm. Parasitization of the tomato fruit worm, cabbage looper, and horn worm eggs in 1968 averaged 81.2, 58.7, and 76.8%, respectively, in the release field compared to 74.9, 42.1, and 81.4% in the control. Most of the egg parasitization in both fields was by T. pretiosum. Of 13,136 and 14,810 fruit examined in the release and control fields, respectively, in 1968, 1.6 and 2.9% were injured by the tomato fruit worm. In 1969, parasitization of the tomato fruit worm, cabbage looper, and horn worm eggs averaged 64.4, 39.0, and 57.7%, respectively, in the release field compared with 42.4, 9.9, and 45.2% in the control. Parasitization of the tomato fruit worm, cabbage looper, and horn worm eggs was about 5, 7, and 10 times higher, respectively, in the release field than that in the control for the first 6 weeks. Of 8454 and 7714 fruit examined in 1969 in the release and control fields, respectively, 2.1 and 7.2% were injured by the tomato fruit worm.