Earthworms are particularly important soil macroinvertebrates and are often used in assessing the general impact of pesticide pollution in soil. The present study was conducted in order to investigate the toxicity of three insect growth regulators (IGRs) buprofezin, lufenuron, and triflumuron, at different application rates and exposure times toward mature earthworms Aporrectodea caliginosa. The effects of these pesticides on the growth rate in relation to the activities of acetylcholinesterase (AChE) and glutathione S-transferase (GST) as biochemical indicators were evaluated to elucidate the mechanisms of action. Toxicity studies indicated that lufenuron was the most harmful pesticide to mature earthworms, followed in descending order by buprofezin and triflumuron. A reduction in growth rate in all pesticide-treated worms was dose-dependent over the 28-day exposure period, which was accompanied by a decrease in AChE and GST activities. Relationships between growth rate, AChE, and GST provided strong evidence for the involvement of pesticidal contamination in the biochemical changes in earthworms, which can be used as a bioindicator of soil contamination by pesticides. 1. Introduction Insect growth regulators (IGRs) as third-generation insecticides have a specific mode of action on insects and a lower toxicity against vertebrates than the conventional insecticides [1–4]. However, heavy applications of such pesticides in agricultural areas may also impact not only on the target species but also on nontarget organisms in and adjacent to the target areas. The concern specifically addressed in the present study relates to the possible effects of pesticides on nontarget soil organisms such as earthworms. Earthworms were chosen as example of nontarget soil organisms due to their beneficial role in the soil and their very low abundance in the orchards and in the adjacent areas [5]. Earthworms are particularly important soil macroinvertebrates and are often used in assessing the general impact of heavy metal and pesticide pollution in soil [6, 7]. Macroinvertebrates have the ability to preserve and contribute to the overall productivity of the soil ecosystem by maintaining soil structure and by regulating the turnover of organic matter [8]. Earthworms feed, cast, and burrow in soil and are exposed to soil contaminants via their intestine or skin [9]. It is also easy to quantify life-cycle parameters of earthworms, accumulation and excretion of pollutants, and biochemical responses [10]. Although the toxicity of pesticides on earthworms in contaminated soil has
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