UAV-Assisted Insecticide Application in Maize: Field Assessment of Yield, Mycotoxin Occurrence and Trichogramma Activity

European corn borer (ECB), Ostrinia nubilalis Hübner, 1796 (Lepidoptera: Pyralidae), is an important maize pest in Serbia and the wider Western Balkan region, where chemical control remains a common management practice. This study evaluated the effects of insecticide treatments applied by an unmanned aerial vehicle (UAV) under field conditions during a single growing season, with emphasis on maize yield, mycotoxin occurrence and the activity of naturally occurring Trichogramma spp. Field trials were conducted in 2023 using four maize hybrids and three treatments: a selective insecticide (spinetoram), a broad-spectrum insecticide (deltamethrin), and a water-only treatment, all applied using the same UAV-based application system. Spray deposition was assessed using water-sensitive papers, while ECB egg masses and Trichogramma parasitism were monitored during the growing season. The results showed that maize yield was primarily influenced by hybrid performance, with insecticide effects depending on treatment selectivity and hybrid response. Under the tested conditions, spinetoram resulted in higher yields than deltamethrin and the water treatment, whereas deltamethrin did not provide a yield advantage over the water-only treatment. Selective insecticide application was also associated with higher observed Trichogramma parasitism compared with the broad-spectrum treatment. Treatment-related differences were observed for selected mycotoxin parameters, including lower fumonisin B1 concentrations in the spinetoram treatment, although responses were not consistent across all analyzed mycotoxins. For HT-2 toxin and T-2 toxin, treatment-related differences were observed in their occurrence, but not in their concentrations. The findings provide field-based evidence on the performance of UAV-assisted insecticide application under the specific climatic, agronomic and pest-pressure conditions of the experiment. Under these conditions, the results indicate that insecticide selectivity and hybrid-specific responses are relevant considerations when evaluating IPM-oriented maize protection strategies, while further multi-location and multi-season studies are required to determine the stability and broader applicability of the observed effects.