Effects of the novel HPPD-inhibitor herbicide QYM201 on enzyme activity and microorganisms, and its degradation in soil.

QYM201 is a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibiting herbicide recently registered in China for controlling grass and broadleaf weeds in wheat. It is a novel herbicide, and its potential harm to soil ecosystems has not yet been reported. This study investigates the influence of QYM201 on soil enzyme activity and microorganism quantities in two different soils at concentrations of 0.1, 1, and 5 mg kg-1 soil. Results indicate that QYM201 initially inhibited soil protease, urease, and sucrase activity and this effect increased with concentration. During the later stages of incubation, inhibitory effects gradually weakened and by the end of the experiment (45 days), enzyme activity was restored to control levels. Catalase activity was stimulated by QYM201, with significant differences observed between the QYM201-treated groups and the control at the onset of exposure. This stimulation effect decreased during the later stages of the experiment. However, catalase activity was still significantly higher at the end of the experiment compared to the control. The effects of QYM201 on soil microorganisms differed. Initially, bacteria and actinomycetes quantities were decreased by QYM201 (10 days). As the incubation progressed, microorganism quantities in the lower concentration groups (0.1 and 1 mg kg-1 soil) were restored to control levels, while those of the high concentration group (5 mg kg-1 soil) did not fully recover. QYM201 did not significantly impact the quantity of fungi. The half-life and degradation rate constant (k) of QYM201 for the two studied soil types were 23.1 days and 16.1 days, and 0.030 and 0.043 day-1, respectively.

Compatibility of chlorantraniliprole with the generalist predator Coccinella septempunctata L. (Coleoptera: Coccinellidae) based toxicity, life-cycle development and population parameters in laboratory microcosms.

Coccinella septempunctata is a common insect predator that provides biological control of many destructive arthropod pests. An assessment of the toxicity of pesticides to predators is a necessary component of Integrated Pest Management (IPM) strategies. In order to evaluate the risks of field insecticide application, we studied the influence of chlorantraniliprole on C. septempunctata larvae using different exposure doses. Chlorantraniliprole exhibited low contact toxicity against 2nd instar larvae of C. septempunctata with the LR50 was 482.7063 g a.i. ha-1 by after a 72-h exposure. In a long-term test, the LR50 of chlorantraniliprole for C. septempunctata decreased from 88.97 to 58.22 g a.i. ha-1, while the hazard quotient (HQ) values were below the threshold value of 2 during the entire observation period. This indicated a low toxicity risk from insecticide exposure. The total effect (E) suggested that chlorantraniliprole could be classified as harmless/slightly harmful to C. septempunctata below/at 200% of the MRFR (the manufacturer maximum recommended field rate) of 120 g a.i. ha-1. We also determined no observed effect application rates (NOERs) of chlorantraniliprole on survival (7.5 g a.i. ha-1), developmental time (15 g a.i. ha-1) and fecundity (30 g a.i. ha-1). Chlorantraniliprole significantly reduced the pupation rate, adult emergence, egg hatchability, and predation success. Population parameters, including R0, r, λ, and T were significantly affected when C. septempunctata were treated with chlorantraniliprole at higher label rates. These results demonstrated that the use of chlorantraniliprole may reduce C. septempunctata population levels and the level of biological control provided by this species.