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Trichogramma Westwood egg parasitoids alone generally fail to suppress heliothine pests when released in established cotton-growing regions. Factors hindering their success include indiscriminate use of detrimental insecticides, compensation for minimal pest larval hatch due to their activity via reduced larval cannibalism or mortality in general, singly laid heliothine eggs avoiding detection and asynchronous development benefiting host over parasitoid. Yet, despite these limitations, relatively large Trichogramma pretiosum Riley populations pervade and effectively suppress Helicoverpa (Hardwick) pests in Australian Bt ( Bacillus thuringiensis Berliner)-transgenic cotton, Gossypium hirsutum L., crops, especially in the Ord River Irrigation Area (ORIA) of tropical northern Australia, where their impact on the potentially resistant pest species, Helicoverpa armigera (Hübner), is considered integral to the local insecticide resistance management (IRM) strategy for continued, sustainable Bt-transgenic cotton production. When devoid of conventional insecticides, relatively warm and stable conditions of the early dry season in 'winter' grown ORIA Bt-transgenic cotton crops are conducive to Trichogramma proliferation and biological control appears effective. Further, there is considerable scope to improve Trichogramma's biological control potential, in both the ORIA and established cotton-growing regions, via habitat manipulation. It is proposed that Trichogramma may prove equally effective in developing agricultural regions of monsoonal northern Australia, and that environmental constraints on Trichogramma survival, and those of other natural enemies, require due consideration prior to their successful application in biological control programs. [ABSTRACT FROM AUTHOR]

Trichogramma limit pest damage to crops by killing the developing embryo of their insect host at the egg stage. Their impact on the potentially insecticide resistant species, Helicoverpa armigera (Hübner), is considered integral to the resistance management plan for transgenic cotton production in the Ord River Irrigation Area in northern Western Australia. The dominant species of egg parasitoid in Ord River Irrigation Area cotton crops is the introduced Trichogramma pretiosum (Riley). Surveys of similar northern Australian regions earmarked for agricultural expansion revealed that T. pretiosum has been introduced, or has adventitiously dispersed, to all developing agricultural regions of northern Australia. Several previously unsequenced species were collected during surveys in more pristine habitats. Trichogramma pretiosum demonstrates an apparent ability to supersede native Trichogramma species and is perhaps favoured by agricultural expansion. [ABSTRACT FROM AUTHOR]