Safety and Sublethal Effects of Acaricides on Stethorus punctillum, a Neglected Key Natural Enemy of Phytophagous Mites

Abstract

Stethorus punctillum Weise, a predatory beetle attacking phytophagous mites in northwest China, remains underutilized for biological control. Current over-reliance on synthetic acaricides necessitates evaluation of their non-target effects on this predator, particularly their safety and sublethal impacts. Here, we assessed the acute toxicity of four acaricides to S. punctillum in laboratory bioassays and then focused on sublethal impacts of abamectin on adult predation efficiency and lifespan. Based on the LC50 values, the acute toxicities of the four acaricides tested against S. punctillum larvae and adults both ranked as follows (from greatest to least): abamectin > pyridaben > spirotetramat > petroleum oil. All acaricides exhibited selective toxicity (STR: 2.16–182.49) with moderate to low risk (SF: 0.46–8.71). Notably, petroleum oil, despite showing the lowest acute toxicity to S. punctillum, posed the highest risk to larvae (SF: 0.46–0.77). Abamectin exposures at LC20 or LC50 significantly compromised S. punctillum adults, prolonging prey handling time (females: 33–100%; males: 40%), reducing maximum daily predation (females: 25–50%; males: 29%), and shortening adult lifespan (females: 2.34–3.17 days; males: 3.95–5.08 days). This study assessed the safety of four commonly used acaricides for S. punctillum, revealing abamectin-induced impairments to key biological traits. Our findings offer critical insights for risk-aware acaricide selection and integrated spider mite management strategies in agroecosystems in northwest China.