We evaluated the response of soil bacteria to applications of the insecticide teflubenzuron at the field rate dosage (FR; 0.15 mg/kg of soil) and at a higher dosage (10*FR; 1.5 mg/kg of soil). When applied at the FR dosage, teflubenzuron had no effect on several biochemical parameters of the soil, including substrate-induced respiration (SIR), dehydrogenase (DHA) and phosphatase activities (PHOS), and N-NO(3)(-) and N-NH(4)(+) concentrations. Additionally, no differences were observed in the culturable fraction of the soil bacteria (the number of heterotrophic, nitrifying, denitrifying and N(2)-fixing bacteria; the growth strategy; the ecophysiological and colony development indices; and the physiological state). In contrast, treatment with the 10*FR dosage of the insecticide significantly increased SIR, DHA, PHOS and N-NH(4)(+) levels and the number of heterotrophic and denitrifying bacteria. Decreases in urease activity (URE) and the number of nitrifying and N(2)-fixing bacteria were also observed. A phospholipid fatty acid (PLFA) method-based analysis of the entire soil microorganism population revealed that teflubenzuron treatment affected the total fatty acid level as well as those considered to be of Gram-positive bacteria, Gram-negative bacteria and fungi. This effect was observed on days 1 and 14 post-treatment. A principal component analysis (PCA) of the PLFAs showed that teflubenzuron treatment significantly shifted the microbial community structure; however, all of the observed effects were transient. Studies on the degradation of teflubenzuron revealed that this process is characterised by a short lag phase and a rate constant (k) of 0.020/day. This degradation rate follows first-order kinetics, and the DT50 was 33.5 days. This is the first study that thoroughly examines the functional and structural status of both the culturable and non-culturable fractions of the soil microbial community after teflubenzuron application.
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