Oviposition and Development of Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) in Three 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 pretiosum (Riley). The southwestern corn borer egg types compared were fertile and infertile fresh stage eggs (<24 h old), red-bar stage eggs (48-72 h old), and black-head stage eggs (96-120 h old). The study consisted of free-choice, no-choice, and paired comparison tests. The paired comparison tests were run under light and no-light conditions to determine the importance of visual cues in host age discrimination. In the free-choice test, eggs in the black-head stage were parasitized significantly less frequently than eggs in any of the other 3 stages. When presented with paired choices of egg types, T. pretiosum females parasitized black-head stage eggs significantly less than other egg types. This non-preference for black-head stage eggs was substantially reduced under dark conditions. When T. pretiosum was limited to 1 egg type as a potential host, they still showed a distinct nonpreference for black-head stage eggs. However, offspring resulting from black-head eggs appeared to be as viable as offspring that developed in other egg types.