Toxicological, morphological and cytochemical effects caused by the agrochemical Fastac Duo in africanized Apis mellifera tolerant to neonicotinoid thiamethoxam

Abstract

Agriculture is one of the main bases of the Brazilian economy, its production of cereals, legumes and oilseeds is breaking records. This great productivity needs handling and care to maintain itself. Due to the occurrence of pests there is a need to use agrochemicals, which in addition to their direct effect on killing insect pests, also affects the viability of beneficial insects to Apis mellifera bees. These insects play an essential role in the pollination of many species. These pollinators have declined for at least 14 years due to several factors, including the large-scale use of agrochemicals. Thus, our research group is maintaining colonies of A. mellifera bees tolerant to the neonicotinoid thiamethoxam, given the importance of this agrochemical in pest control. Due to the high number of available agrochemicals, in the present study the toxicity, changes in chromatin and morphology of the midgut of workers A. mellifera F4 tolerant to thiamehtoxam, submitted to oral exposure with the agrochemical Fastac Duo (combination of acetamiprid and alpha -cipermethrin). Adult forage workers of A. mellifera F4 tolerant were collected and submitted to in vitro bioassays, by oral exposure for 24 and 72 hours. After this period, the workers were analyzed to check for mortality, dose/response ratio, using the cytochemical technique Critical Electrolyte Concentration (CEC). The most digestion occurs in bees to observe the morphology of this region of the digestive tract. The results showed that there was a high mortality of workers in the treatments performed indicating that there is no cross tolerance, that is, F4 is not tolerant to Fastac Duo, but there is a positive dose/response correlation, where the higher the dose used, the greater the mortality. The changes in the chromatin structure suggest that there is condensation of the chromatin and a decrease in gene expression in two concentrations analyzed at 24 and 72 hours. As for the morphology of the midgut, changes were detected at the cellular level, but the peritrophic membrane was preserved. Thus, the use of Fastac Duo should be avoided, or at least, used in minimum doses necessary to avoid the mortality of A. mellifera bees.