The bulb mite, Rhizoglyphus robini, is one of the important pests that cause significant damage to various products at the field as well as storage, including the strategic product of saffron. The need for chemical control is often inevitable to protect agricultural products against pests. In addition to direct lethal effects of pesticides, their sublethal effects on the arthropod biology and physiology should be eva‎luated. One of the responses to insecticides is the stimulation of biological processes by inducing hormesis, a term which is used to describe the stimulatory effects of mild to moderate levels of stressors (including pesticides). This phenomenon can be a possible cause of secondary pest outbreaks and target pest resurgence. Neonicotinoid insecticides are one of the most frequently used pesticides which may lead to stimulant effects in the affected insects and mites. Thus in this study, first, we determined the effects of sublethal doses of three neonicotinoids, imidacloprid, thiamthoxam and dinotefuran, on the reproduction of R. robini, at 24, 48, 72 and 96 hours after treatment. Based on the results, the highest number of eggs compared to the control was observed in imidacloprid at 70 and 140 mg a.i./l concentrations at 24 hours after treatment (HAT), so biological and physiological impacts of imidacloprid were subsequently eva‎luated. Despite of the stimulating effects of imidacloprid on the mite reproduction, no significant differences were observed in the offspring (F1) biological aspects including egg hatch rate, embryonic period and sex ratio, while an increase was found in the preimaginal period of imadacloprid treated F1 mites. In addition to their important roles in the metabolism of insecticides in insects and mites, detoxification enzymes such as cytochrome P450 monooxygenases, Glutathione S-transferases, and esterases are capable to respond to chemical stresses through increasing enzyme activity a process known as enzyme induction. eva‎luation of the detoxification enzyme activities at 0 and 48 HAT with imidacloprid, showed that the highest activities of esterases and glutathione S-transferases were determined at 70 mg a.i./l and for cytochrome P450s at 140 mg a.i./l, all at 0 HAT. Also, an increase in the activity of antioxidant enzyme catalase was observed in treated mites at 0 and 48 HAT compared to that of control. Considering that imidacloprid exposure induced an increase in the egg production in the early hours after treatment, it seems that there is a correlation between increased reproduction and induced activity of detoxification enzymes. Physiologically, lipids and carbohydrates are essential for the growth, development and movement of insects, and the improvement of physiological processes can also be related to hormesis. In this study, a significant increase in the lipid content of R. robini was observed at the hormetic doses of 140 and 70 mg a.i./l. Lipids in insects are considered as capital for reproduction, and high lipid content generally translates into high fecundity potential. In addition to being the main source of energy storage in insects, fat bodies also mediate metabolism in insects, which produce and store many of the enzymes involved in insecticide detoxification. In this study, we also showed that after imidacloprid pretreatment at a concentration of 140 mg a.i./l. and activating the detoxification pathways, diazinon susceptibility (based on the LC50 values) was significantly declined (two-fold). The result of this study can provide useful information to develop suitable rotations or mixtures of pesticides, since hormesis-inducing pesticides may cause not only control failure of the pest but also might contribute to the higher tolerance of other pesticides.

جهانگير خواجه علي

نفيسه پورجواد، محمد حسين اهتمام