Persistence of desiccant herbicides applied to transgenic maize on Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae)

Maize is one of the most cultivated cereals in the world, and in order to obtain high yields adequate weed control is essential. However, the use of herbicides may compromise the beneficial effects of the actions of natural enemies, among them the egg parasitoid Trichogramma pretiosum. The aim of this study was to estimate the duration of the harmful activity of desiccant herbicides applied to transgenic maize on the parasitoid T. pretiosum through persistence testing. Bioassays were carried out in the laboratory, where the adult parasitoids were exposed to herbicide residue following the methods proposed by the 'International Organisation for Biological Control of Noxious Animals and Plants1 (IOBC). The herbicides were sprayed onto the leaves of plants of transgenic maize, which were taken to the laboratory for the construction of cages where adults of T. pretiosum were exposed to 3, 10, 17, 24 and 31 days after application. A completely randomised design was used with four replications per treatment. The reduction in parasitism relative to the control was used to classify the pesticides for selectivity and then for persistence. The desiccant herbicides based on isopropylamine salt (Glifosato (R) Atanor 48, Gli-Up (R) 480 SL, Roundup (R) Original, Roundup (R) Transorb, Roundup (R) WG, Shadow (R) 480 SL, Stinger (R) and Trop (R)), potassium salt (Zapp (R) Qi 620) and ammonium salt (Finale (R)) were considered to be short-lived, with less than five days of harmful activity against the parasitoid. Extremely large releases of T. pretiosum can therefore be carried out three days after spraying these desiccant herbicides.