Parasitism of Heliothis zea (Lepidoptera: Noctuidae) Eggs: Effect on Pest Management Decision Rules for Processing Tomatoes in the Sacramento Valley of California

Abstract

Egg parasitism of Heliothis zea (Boddie) and other lepidopterous pests was monitored in a field trial of processing tomato cultivars in 1981 and in several late-season commercial fields of processing tomatoes in the Sacramento Valley of California in 1983, 1985, and 1986. Four species of Trichogramma were present: T. pretiosum Riley, T. thalense (Pinto & Oatman), T. deion Pinto & Oatman, and T. brevicapillum Pinto & Platner. Actual parasitism of H. zea eggs exceeded 83% in all fields monitored in 1985 and exceeded 62% in most fields monitored in 1986. Manduca spp. and Trichoplusia ni (Hübner) eggs were also commonly parasitized by Trichogramma spp. The high levels of H. zea egg parasitism recorded in these commercial fields indicates that the current economic threshold, which is based on the abundance of white H. zea eggs, can be increased to account for the mortality caused by Trichogramma. Procedures to incorporate H. zea egg parasitism into the current integrated pest management program for processing tomatoes are proposed. Acceptable fruit quality at harvest in fields that exceeded the current economic threshold during the growing season provides additional support for increasing the threshold. The effect of insecticide applications on H. zea egg parasitism is discussed.