Toxicidade de fungicidas utilizados na cultura do milho para o predador Doru luteipes (dermaptera: forficulidae)

Abstract

Maize crops are attacked by pests and diseases that compromise both grain quality and productivity. Among the main insect pests of this crop is Spodoptera frugiperda (Lepidoptera: Noctuidae), whose control is mainly carried out using chemical insecticides and Bt technology. However, populations of this pest can also be naturally regulated by naturally occurring natural enemies, such as the earwig Doru luteipes (Dermaptera: Forficulidae). Diseases, in turn, are mainly controlled with synthetic fungicides, which may cause biological imbalances in maize fields. Therefore, it is important that integrated pest management (IPM) programs consider the impact of pesticides on natural enemies.The aim of this study was to evaluate the toxicity of fungicides recommended for maize crops to fourth-instar nymphs (N4) and adults of D. luteipes via different exposure routes. The fungicides and their respective doses were: chlorothalonil (10.0 g/L); pyraclostrobin + epoxiconazole (5.0 mL/L); pyraclostrobin + fluxapyroxad (2.3 mL/L); mancozeb (14.0 g/L); azoxystrobin + carboxamide (1.0 g/L); azoxystrobin + difenoconazole (5.0 mL/L); and thiophanate-methyl (0.35 g/L). Negative and positive controls were distilled water and an insecticide based on Beauveria bassiana (3.25 mL/L), respectively. Fungicide applications were carried out using a Potter spray tower calibrated at 15 lb/in2 to apply 1.5 ± 0.5 μL/cm2. The exposure routes evaluated were: (i) topical application; (ii) contact with residues; (iii) ingestion of contaminated prey; and (iv) persistence on inert surfaces. The bioassays were conducted in a completely randomized design with 50 insects per treatment (10 insects per replicate). Daily mortality, egg viability, and nymph viability were assessed for all treatments. For adults, fungicides applied topically did not reduce the median lethal time (LT50). Treatments with pyraclostrobin, pyraclostrobin + epoxiconazole, and B. bassiana showed high toxicity to nymphs and adults of D. luteipes, whereas chlorothalonil and thiophanate-methyl were selective, with lower effects on survival. Toxicity varied according to the exposure route: contact with residues on inert surfaces caused greater negative effects, while ingestion of contaminated prey proved less harmful to the predator. Based on these results, it is inferred that D. luteipes exhibits natural resistance to some compounds, possibly linked to morphological characteristics and detoxification mechanisms. The fungicides evaluated showed selectivity to the predator D. luteipes, with variable toxicity depending on the exposure route. Residues of pyraclostrobin + epoxiconazole, azoxystrobin + difenoconazole, and mancozeb were lethal to nymphs and adults, whereas most products were classified as short-lived. Ingestion of contaminated prey had a lower impact on survival, and due to their high toxicity, pyraclostrobin + epoxiconazole, pyraclostrobin + carboxamide, mancozeb, and thiophanate-methyl should not be preferred for applications in maize fields when the conservation of the predator D. luteipes is intended.