Laboratory Toxicity and Field Efficacy of Four Microbial-Derived Pesticides Combined with Two Adjuvants Against Lygus pratensis (Hemiptera: Miridae)

Simple SummaryIn the cotton-growing regions of Xinjiang, China, extensive reliance on conventional insecticides has promoted the development of resistance inLygus pratensis, making its management increasingly challenging. Moreover, excessive pesticide applications have resulted in environmental contamination, pesticide residues, and increased ecological risks. In this study, we evaluated four kinds of microbial-derived pesticides (abamectin, emamectin benzoate,Beauveria bassiana, andMetarhizium anisopliae) mixed with two adjuvants—d-limonene and mineral oil—for the control ofL. pratensis. The results showed that a 30% reduction in the application rate of these pesticides, when combined with appropriate adjuvants, achieved control efficacy comparable to or numerically higher than the corresponding full-rate pesticide treatments, with no significant efficacy loss observed. Notably, reduced-rate treatments combined with adjuvants showed numerically earlier efficacy onset for the two fungal biocontrol agents, which normally act slowly. This study provides a feasible and environmentally friendly strategy to reduce pesticide inputs and achieve sustainable management ofL. pratensisin cotton fields.Systematic field data on adjuvant-amended microbial-derived pesticides againstL. pratensisin arid, high-ultraviolet cotton regions remain scarce. This study systematically evaluated the laboratory toxicity and field efficacy of four kinds of microbial-derived pesticides (abamectin, emamectin benzoate,B. bassiana, andM. anisopliae) and their combinations with adjuvants againstL. pratensisin Xinjiang cotton fields. As a comprehensive regional study, this work elucidates the differential enhancement patterns of d-limonene and mineral oil on antibiotic insecticides and entomopathogenic fungi, providing targeted field data for pesticide reduction strategies. The laboratory toxicity of seven microbial-derived pesticides was determined using the leaf-tube residual film method. Four effective agents were selected and combined with d-limonene or mineral oil for field efficacy trials. Abamectin and emamectin benzoate exhibited rapid and high insecticidal activity, with 48 h LC50values of 1.198 mg/L and 3.424 mg/L, respectively. The two entomopathogenic fungi exhibited slower insecticidal activity than the chemical insecticides but maintained relatively stable control effects throughout the observation period. In field trials, when abamectin or emamectin benzoate was applied at a 30% reduced rate in combination with mineral oil or d-limonene, the control efficacy was equivalent to or higher than that of the full-rate application of the pesticide alone. The treatment of abamectin (4.20 g a.i./hm2) plus mineral oil achieved the highest control efficacy (89.24%) at 3 days post-treatment. ForB. bassianaandM. anisopliae, reduced-rate adjuvant-amended treatments showed numerically higher initial and residual efficacy than the full-rate single-agent fungal treatments. The treatment ofM. anisopliae(7.35 × 1012spores/hm2) plus d-limonene reached 70.50% efficacy at 7 days post-treatment, which was significantly higher than that of the full-rate fungal treatment alone. No phytotoxicity symptoms were observed on cotton plants. Under the tested conditions, the rational combination of microbial-derived pesticides with appropriate adjuvants demonstrates the potential for a 30% reduction in pesticide dosage while maintaining or improving field efficacy, providing region-specific reference for the sustainable management ofL. pratensisin Xinjiang cotton fields.