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Acephate (organophosphate) is frequently used to control piercing/sucking insects in field crops in southern United States, which may pose a risk to honey bees. In this study, toxicity of acephate (formulation Bracket ® 97) was examined in honey bees through feeding treatments with sublethal (pollen residue level: 0.168 mg/L) and median-lethal (LC 50 : 6.97 mg/L) concentrations. Results indicated that adult bees treated with acephate at residue concentration did not show significant increase in mortality, but esterase activity was significantly suppressed. Similarly, bees treated with binary mixtures of acephate with six formulated pesticides (all at residue dose) consistently showed lower esterase activity and body weight. Clothianidin, λ-cyhalothrin, oxamyl, tetraconazole, and chlorpyrifos may interact with acephate significantly to reduce body weight in treated bees. The dose response data (LC50: 6.97 mg/L) revealed a relatively higher tolerance to acephate in Stoneville bee population (USA) than populations elsewhere, although in general the population is still very sensitive to the organophosphate. In addition to killing 50% of the treated bees acephate (6.97 mg/L) inhibited 79.9%, 20.4%, and 29.4% of esterase, Glutathione S-transferase (GST), and acetylcholinesterase (AChE) activities, respectively, in survivors after feeding treatment for 48 h. However, P450 activity was elevated 20% in bees exposed to acephate for 48 h. Even though feeding on sublethal acephate did not kill honey bees directly, chronic toxicity to honey bee was noticeable in body weight loss and esterase suppression, and its potential risk of synergistic interactions with other formulated pesticides should not be ignored., (Published by Elsevier Inc.)

Organophosphate pesticide diazinon is a specific inhibitor of acetylcholinesterase (AChE), which is a common neurotoxicity biomarker in environmental studies. In honeybees, AChE exists in two forms having different physiological roles, one existing as a soluble form and the other as membrane-bound. In most studies AChE activity has been analysed without paying considerable attention to different forms of AChE. In this study, we exposed honeybees Apis mellifera carnica for 10days to diazinon via oral exposure and analysed the total AChE activities in salt soluble (SS) and detergent soluble (DS) fractions. We assumed that SS fraction would preferentially contain the soluble AChE, but the DS fraction would contain only membrane AChE. On the contrary, our results showed that SS and DS fractions both contain soluble and membrane AChE and the latter has considerably higher activity. Despite this we obtained a differential response of AChE activity in SS and DS fractions when exposed to diazinon. The head/thorax AChE activity in DS fraction decreased, while the head/thorax AChE activity in SS fraction increased at sublethal concentrations. The AChE activity in honeybee hemolymph shown here for the first time is a salt soluble enzyme. Its activity remained unaltered after diazinon treatment. In conclusion, we provide evidence that varying results regarding AChE activity alterations upon stressor exposure are obtained when extracted through different procedures. In further environmental studies with honeybees this differential response of AChE activity should be given considerable attention because this affects the outcome of ecotoxicity study., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The metabolism and rate of penetration of leptophos (O-methyl O-4-bromo-2,5-dichlorophenyl phenylphosphonothioate) was determined in a susceptible strain and a strain of housefies which was 50-fold resistant to leptophos. Penetration of leptophos into resistant flies was substantially slower than into susceptible flies but large differences in metabolism, both quantitatively and qualitatively, were not observed. No difference was observed in the sensitivity of flyhead and thorax acetylcholinesterase to leptophos-oxon in vitro, and tolerance to leptophos by the resistant strain is explained in terms of decreased rates or penetration and minor differences in metabolism.