Silent effect of the fungicide pyraclostrobin on the larval exposure of the non-target organism Africanized Apis mellifera and its interaction with the pathogen Nosema ceranae in adulthood

The frequent exposure of bees to a wide variety of fungicides, on crops where they forage, can be considered a stressor factor for these pollinators. The organisms are exposed both to the fungicide active ingredients and to the adjuvants of commercial formulations. All these ingredients are brought to the hive by bee foragers through contaminated pollen and nectar, thus exposing also immature individuals during larval phase. This work aimed to compare the effects of larval exposure to the fungicide pyraclostrobin (active ingredient and commercial formulation) and its influence on the cytotoxicity to midguts in adults, which were inoculated with the Nosema ceranae spores in the post-emergence stage. Under laboratory conditions, Apis mellifera larvae received an artificial diet containing fungicide solution from the third to the sixth day of the feeding phase. One-day-old adult workers ingested 100,000 infectious N. ceranae spores mixed in sucrose solution. Effects on midgut were evaluated through cellular biomarkers of stress and cell death. The exposure to the fungicide (active ingredient and commercial formulation) did not affect the larval post-embryonic development and survival of adult bees. However, this exposure induced cytotoxicity in the cells of the midgut, showed by the increase in DNA fragmentation and alteration in the HSP70 immunolabeling pattern. Without the pathogen, the midgut cytotoxic effects and HSP70 immunolabeling of the organisms exposed to the commercial formulation were lower when compared to the exposure to its active ingredient. However, in the presence of the pathogen, the cytotoxic effects of the commercial formulation to the adult bees’ midgut were potentialized. The pathogen N. ceranae increased the damage to the intestinal epithelium of adult bees. Thus, realistic doses of pyraclostrobin present in beebread consumed by larvae can affect the health and induce physiological implications to the midgut functions of the adult bees.