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Among the many causes of pollinator decline, which is a growing ecological and economic problem worldwide, our research aimed to investigate oxidative stress caused by acute pesticide exposure in the central nervous system of honeybees.

Deltamethrin was used throughout the investigation as a representative of the pyrethroid ester insecticide group besides tebuconazole, a triazole fungicide, since these compounds are widely and extensively used in modern agriculture. After gathering the honeybee subjects and forming the test along with the control groups, the aforementioned substances were administered in sublethal doses (deltametrin: LD50/10 = 7,9 ng/bee/day, LD50/20 = 3,95 ng/bee/day, LD50/40 = 1,975 ng/bee/day, tebukonazol: LD50/10 = 8,505 μg/bee/day, LD50/20 = 4,253 μg/bee/day, LD50/40 = 2,123 μg/bee/day) during a 48-hour period through the feeding solution. In this study, tissue samples obtained after preparation of the central nervous system were homogenized and colorimetric measurements were performed for the following parameters: malondialdehyde (MDA) concentration, superoxide dismutase (SOD) and glucose-6-phosphate dehydrogenase (G6PDH) enzyme activity, as well as reduced and oxidized glutathione ratio (GSH-GSSG).

The results for almost all parameters supported the presence of oxidative stress for both tested substances. The MDA concentrations, which were used as a marker of lipid peroxidation, were significantly elevated by the highest tested dosages of deltamethrin and tebuconazole. In addition, a significantly decreased SOD enzyme activity was observed compared to the control group in every test group except for the one with the highest dose of deltamethrin, and since this enzyme serves as one of the most potent antioxidants in the first line of redox defense mechanisms, it can indicate a disturbance or slowing down of the antioxidant system, which may point to an increased risk of oxidative stress. The GSH-GSSG ratio significantly decreased in all test groups, which represents the oxidation processes taking place in the cerebral ganglion as well as the depletion of the glutathione system, which plays a key role in redox homeostasis. Furthermore, a significant decrease was observed in the activity of G6PDH, which is a key enzyme in the pentose phosphate pathway. These inhibitory effects may also contribute to the depletion of the glutathione system.

Our results confirm the hypothesis that deltamethrin and tebuconazole may lead to increased levels of oxidative stress in the central nervous systems of honeybees, which can contribute to the development of a number of major health problems, such as colony collapse disorder, which still has an unknown etiology and results in the disappearance of bees.