Apis mellifera perform important pollination roles in agroecosystems. However, there is often intensive use of systemic pesticides in crops, which can be carried to the colony by forage bees through the collection of contaminated pollen and nectar. Inside the colony, pollen loads are stored by bees that add honey and several enzymes to this pollen. Nevertheless, intra-colonial chronic exposure could induce sublethal effects in young bees exposed to a wide range of pesticides present in these pollen loads. This study was aimed to both determine the survival rate and evaluate the sublethal effects on the hepato-nephrocitic system in response to continuous oral exposure to lower concentrations of neonicotinoid thiamethoxam (TXT) and picoxystrobin fungicide (PXT). Exposure to a single chemical and co-exposure to both pesticides were performed in newly emerged honeybee workers. A significant decrease in the bee survival rates was observed following exposure to TXT (0.001 ng a.i./μL) and PXT (0.018 ng a.i./μL), as well as following co-exposure to TXT+PXT/2. After five days of continuous exposure, TXT induced sub-lethal effects in the organs involved in the detoxification of xenobiotics, such as the fat body and pericardial cells, and it also induced a significant increase in the hemocyte number. Thus, the hepato-nephrocitic system (HNS) reached the greatest level of activity of pericardial cells as an attempt to eliminate this toxic compound from hemolymph. The HNS was activated at low levels by PXT without an increase in the hemocyte number; however, the mobilization of neutral glycoconjugates from the trophocytes of the fat body was prominent only in this group. TXT and PXT co-exposure induced intermediary morphological effects in trophocytes and pericardial cells, but oenocytes from the fat body presented with atypical cytoplasm granulation only in this group. These data showed that the realistic concentrations of these pesticides are harmful to newly emerged Africanized honeybees, indicating that intra-colonial chronic exposure drastically reduces the longevity of bees exposed to neonicotinoid insecticide (TXT) and the fungicide strobilurin (PXT) as in single and co-exposure. Additionally, the sublethal effects observed in the organs constituting the HNS suggest that the activation of this system, even during exposure to low concentrations of theses pesticides, is an attempt to maintain homeostasis of the bees. These data together are alarming because these pesticides can affect the performance of the entire colony.

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Bees are valuable bioindicators, providing information regarding environmental conditions through different kinds of analyses. Therefore, the effect of cadmium on the morphology of ovaries of Bombus morio workers was used to study a concentration considered environmentally safe (1 ppb) in Brazil. Workers of the same estimated age exposed for 48 h to 1 ppb cadmium showed extensive morphological changes in the germarium and vitellarium compared with the control group. Bees exposed to cadmium showed death of or damage to entire vitellogenic follicles, with chromatin condensation and fragmentation of nurse cell nuclei. In the germarium, the intercellular bridge connecting the primary oocyte to the developing nurse cells was broken. The nurse cells formed a cluster of cells with compacted chromatin, detached from an isolated primary oocyte. In some cases, the cytoblasts were absent from the germarium, leaving an empty space surrounded by collapsed peritoneal sheaths. We further propose that such a hazardous impact of 1 ppb cadmium on the ovaries of B. morio workers is not only mainly due to cadmium itself as an endocrine disruptor, indirect oxidative stress promoter, cytoskeleton destabilizer and mutagenic trace metal, but by disruption of the trophocytes, where perivitelline space filled with eosinophil material in the control group, was totally empty in exposed bees, suggesting interruption of trophocyte vitellogenin production.

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