Trichogramma pretiosum Riley was released in the field for suppression of corn earworm, Heliothis zea (Boddie), egg populations in Nova Scotia in 1985–1987. Trichogramma pretiosum reduced com earworm populations 7.4–53% compared with chemical treatments reductions of 19–100%. Trichogramma pretiosum were not as effective as insecticides, especially when populations of the corn earworm were low (less than five larvae per 1000 ears). Timing of T. pretiosum releases and spray applications were determined by blacklight trap catches and were considered critical for effective control.