Assessing the effects of a commercial fungicide and an herbicide, alone and in combination, on Apis mellifera: insights from biomarkers and cognitive analysis

Abstract

Agrochemicals play a vital role in protecting crops and enhancing agricultural production by reducing threats from pests, pathogens and weeds. The toxicological status of honey bees can be influenced by a number of factors, including pesticides. While extensive research has focused on the lethal and sublethal effects of insecticides on individual bees and colonies, it is important to recognise that fungicides and herbicides can also affect bee health. Unfortunately, in the field, honey bees are exposed to mixtures of compounds rather than single substances. This study aimed to evaluate the effects of a commercial fungicide and a commercial herbicide, both individually and in combination, on honey bees. Mortality assays, biomarkers and learning and memory tests were performed, and the results were integrated to assess the toxicological status of honey bees. Neurotoxicity (acetylcholinesterase and carboxylesterase activities), detoxification and metabolic processes (glutathione S-transferase and alkaline phosphatase activities), immune system function (lysozyme activity and haemocyte count) and genotoxicity biomarkers (nuclear abnormalities assay) were assessed. The fungicide Sakura® was found to activate detoxification enzymes and affect alkaline phosphatase activity. The herbicide Elegant 2FD and the combination of both pesticides showed neurotoxic effects and induced detoxification processes. Exposure to the herbicide/fungicide mixture impaired learning and memory in honey bees. This study represents a significant advance in the understanding of the toxicological effects of commonly used commercial pesticides in agriculture and contributes to the development of effective strategies to mitigate their adverse effects on non-target insects.