OVIPOSITION AND DEVELOPMENT OF TRICHOGRAMMA-PRETIOSUM (HYMENOPTERA, TRICHOGRAMMATIDAE) IN 3 AGE CLASSES OF SOUTHWESTERN CORN-BORER EGGS

Laboratory studies were conducted to determine the effect of Diatraea grandiosella Dyar egg age on the parasitism level of Trichogramma pret iosum (Riley). The southwestern corn borer egg types compared were fer tile and infertile fresh stage eggs (<24 h old), red-bar stage eggs (4 8-72 h old), and black-head stage eggs (96-120 h old). The study consi sted of free-choice, no-choice, and paired comparison tests. The paire d comparison tests were run under light and no-light conditions to det ermine the importance of visual cues in host age discrimination. In th e free-choice test, eggs in the black-head stage were parasitized sign ificantly less frequently than eggs in any of the other 3 stages. When presented were paired choices of egg types, T. pretiosum females para sitized black-head stage eggs significantly less than other egg types. This non-preference for black-head stage eggs was substantially reduc ed under dark conditions. When T. pretiosum was limited to 1 egg type as a potential host, they still showed a distinct nonpreference for bl ack-head stage eggs. However, offspring resulting from black-head eggs appeared to be as viable as offspring that developed in other egg typ es.