Assessing the toxicity of selected pesticides to Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) pupae as a first step in the development of a potential novel deployment programme

Trichogramma spp. have been used or have been proposed for use in biological control programmes of lepidopteran pests, including the European corn borer, Ostrinia nubilalis, the cotton bollworm, Helicoverpa armigera, and the spruce budworm, Choristoneura fumiferana. Releases are typically made by placing cards with parasitised eggs at set points in the field. However, this method can be cost-prohibitive due to its laborious nature. As a result, labour-saving mechanised release programmes have been developed, including distribution by spray equipment. However, few have investigated applying Trichogramma with a standard pesticide application (i.e. ‘tank mix’). As a first step to ascertain the feasibility of such a system, we observed the effect of immersion of T. ostriniae pupae in field-relevant concentrations of eight herbicides (bentazon, clethodim, fomesafen, quizalofop, Glacial acetic acid, glyphosate, imazamox, imazethapyr), three fungicides (Copper Hydroxide, flutriafol, and penthiopyrad), one insecticide (K+ salt of fatty acid), and five adjuvants (Ammonium Sulfate, Crop Oil Concentrate, Methylated seed oil, Non-ionic surfactant, and Urea-Ammonium Nitrate) on the emergence of T. ostriniae adults. The herbicides GAA and clethodim; the fungicides copper hydroxide, flutriafol, and penthiopyrad; and the adjuvants COC, MSO, and NIS all reduced T. ostriniae emergence compared to a water control. No emergence was observed with exposure to quizalofop, GAA, or K+ salt of fatty acid treatments. Other treatments did not affect emergence compared to water. Thus, deploying Trichogramma with a standard pesticide application may be a feasible labour-saving distribution method that warrants further investigation.