Seasonal Distribution of Trichogramma (Hymenoptera: Trichogrammatidae) Species Associated with a Maryland Soybean Field

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Abstract
Heliothis virescens (F.) egg cloths were used to sample Trichogramma populations in a 450-m 2 soybean plot and an adjoining 450-m 2 plot of natural, weedy vegetation during 1981 and 1982. Fourteen biparental and one uniparental species were collected, including, in descending order of abundance, T. pretiosum Riley, T. minutum Riley, T. exiguum Pinto and Platner, T. retorridum (Girault), T. marylandense Thorpe, T. parkeri Nagarkatti, and T. nubilale Ertle and Davis. Cross-mating tests determined the existence of a Trichogramma population that is morphologically indistinguishable but reproductively isolated from T. pretiosum . Collections of this new population were only 5% as frequent as those of T. pretiosum . The seasonal distributions of the species are described, and a method for screening field collections of Trichogramma for sibling and cryptic species is presented.