High Tolerance of Trichogramma Pretiosum (Hymenoptera: Trichogrammatidae) to the Mixture of the Herbicides Nicosulfuron Plus Atrazine

Background: Maize, Zea mays (Poaceae), is one of the most important crops in the world, but defoliating caterpillars (Lepidoptera) and weeds can reduce the productivity of this plant. The control of weeds in the maize crop in Brazil is mainly accomplished with nicosulfuron- and atrazine-based herbicides, and of lepidopteran pest eggs with use of several species of Trichogrammatidae (Hymenoptera) parasitoids released. The objective of this study was to evaluate the rates of parasitism and emergence of females and the sex ratio (%) of 10 Trichogrammatidae species, in a free-choice test, submitted to a mixture of the herbicides Sanson 40 SC® (a.i. nicosulfuron; dose: 30 g.ha–1) + Gesaprim 500 Ciba-Geigy® (a.i. atrazine; dose: 1500 g.ha–1) in the laboratory.Results: The parasitism rate (%) of Trichogramma acacioi Brun, Moraes & Soares, Trichogrammatoidea annulata de Santis, Trichogramma atopovirilia Oatman & Platner, Trichogramma bennetti Nagaraja & Nagarkatti, Trichogramma brunni Nagaraja, Trichogramma brasiliensis Ashmead, Trichogramma demoraesi Nagaraja, Trichogramma galloi Zucchi, and Trichogramma soaresi Nagaraja was lower with the herbicide mixture of nicosulfuron + atrazine than the control and, therefore, this mixture was considered to be slightly harmful (i.e., class II of the International Organization for Biological and Integrated Control) to these parasitoids. This solution reduced the emergence rate (%) of female T. acacioi, T. annulata, T. atopovirilia, T. bruni, T. brasiliensis, T. demoraesi, T. galloi, and T. soaresi, being classified as harmless to T. soaresi, moderately harmful to T. galloi and slightly harmful to the other species. The herbicide mixture of nicosulfuron + atrazine reduced the sex ratio of T. acacioi, T. atopovirilia, T. bruni, T. demoraesi, T. galloi, and T. soaresi, being classified as harmless to T. annulata and T. brasiliensis, and slightly harmful to the other species.Conclusions: The biological parameters (i.e., rates of parasitism and emergence and the sex ratio) of T. pretiosum, followed by T. bennetti, T. annulata and T. brasiliensis were the least affected by the herbicide mixture. These species should be chosen for release, on pieces of paperboard with parasitized E. kuehniella eggs, in crops together with the application of nicosulfuron + atrazine.