Sublethal Cypermethrin Toxicity in Apis mellifera: Integrated Biochemical, Oxidative Stress, Neurophysiological and Genotoxic Responses

Abstract

The extensive use of synthetic pyrethroid insecticides in farming practices have ratcheted up the risk of unintentional exposure to invaluable pollinators. The current experiment explored the influence of cypermethrin on adult worker honeybees using a comprehensive approach consisting of acute toxicity, biochemical analyses, enzymatic assessments, neurophysiological examinations, and genetic analysis. The first step was to determine acute toxicity in adult bees via increasing dosages of cypermethrin. Probit method revealed a confidence interval between 8.18mg/L, the lethal concentration at 50 percent for the test organisms, ranging from 7.54–8.87 mg/L. Following that, sub-lethal doses led to biochemical changes in the tissue homogenate. Glucose levels before treatment was measured to be 86.42 mg/dl but dropped to 58.91 mg/dl at the highest concentration of cypermethrin. Total protein showed decreased values, from 61.84 mg/g of tissue to 40.52 mg/g at the lethal concentration. Alkaline phosphatase activity decreased as treatment time increased along with acid phosphatase activity, demonstrating an interference with metabolism and engulfment of membranes through lysosomal processes was initiated. The treatment also impacted lipid metabolism and caused an increase in cholesterol. Acetylcholinesterase activity decreased from an average of 8.94 µmol/min/mg of protein to 4.83 µmol/min/mg of protein showing that neurophysiology was also compromised. Antioxidation was decreased as the dosage increased with reductions in catalase, glutathione, and all other antioxidants. The increase in DNA damage was demonstrated by a number of comet parameters: comet length, the percentage of DNA in the comet, Olive tail moment, and the tail moment. These results conclude that the impact of cypermethrin in honeybees goes far beyond mortality to include various biochemical, physiological, and molecular processes. These biophysiological parameters can be helpful to monitor the stress caused by exposure to sub-lethal levels of pesticide in honey bees.