Among the factors that contribute to the reduction of honeybee populations are the pesticides. These chemical compounds reach the hive through forager bees, and once there, they can be ingested by the larvae. We evaluated the effects of repeated larval exposure to neonicotinoid insecticide, both in isolation and in combination with strobilurin fungicide, at environmentally relevant doses. The total consumption of the contaminated diet was 23.63 ng fungicide/larvae (pyraclostrobin) and 0.2364 ng insecticide/larvae (clothianidin). The effects on post-embryonic development were evaluated over time. Additionally, we assessed the survival pattern of worker bees after emergence, and the pesticides’ effects on the behavior of newly emerged workers and young workers. Young bees that were exposed to the fungicide and those subjected to co-exposure to both pesticides during larval phase showed behavioral changes. The insecticide, both in isolation and in combination with fungicide reduced the bees’ longevity; this effect of larval exposure to pesticides was stronger in bees that were exposed only to the insecticide. Although the larvae did not have sensitivity to exposure to pesticides, they showed later effects after emergence, which may compromise the dynamics of the colony, contributing to the reduction of the populations of bees in agroecosystems.

Bees that forage in agricultural plantations and surroundings are exposed to pesticide residues, which can cause sublethal effects in individuals and consequently compromise the performance of the colony. Regarding the honey bees, beekeepers can be hampered by decreased production of honey and other bee products. Although the effects of insecticides on bees are widely studied for obvious reasons, there is growing evidence that fungicides, too, are not harmless to bees. However, further studies are needed on the effects caused by fungicide residues present in pollen and nectar which are collected and consumed by honey bees. For this reason, we aimed to perform a histopathological diagnosis and cell death immunolabeling in the midgut and Malpighian tubules of Africanized honey bee workers throughout continuous oral exposure (24 h, 48 h, 72 h, 96 h) to low concentrations of picoxystrobin (9 ppb and 18 ppb), a strobilurin fungicide. Although there were no histopathological effects on the Malpighian tubules, an organ that plays a role in excretion, these effects were observed in the midgut of bees exposed to both concentrations of picoxystrobin. Morphological alterations, as well as positive-labeling for cell death, were observed in the midgut of exposed bees over time (from 24 to 96 h after the beginning of exposure). Although the data have shown evidence of intestinal epithelial renewal in response to cytotoxic effects, i.e., recovery after short-time exposure, this organ may have its nutrient absorption functions compromised in the long-term, which may lead to symptoms of malnutrition and affect the individual’s performance, which could, in turn, affect the whole colony.

Managed honey bees are daily exposed in agricultural settings or wild environments to multiple stressors. Currently, fungicide residues are increasingly present in bees’ pollen and nectar and can harm colonies’ production and survival. Therefore, our study aimed to evaluate the effects of the fungicide pyraclostrobin on the fat body and pericardial cells of Africanized honey bees. The foragers were divided into three experimental treatment groups and two controls: pyraclostrobin 0.125 ng/µL (FG1), 0.025 ng/µL (FG2), 0.005 ng/µL (FG3), untreated control (CTL), and acetone control (CAC). After five days of oral exposure (ad libitum), the bees were dissected and prepared for histopathological and morphometric analysis. The FG1-treated bees showed extensive cytoarchitecture changes in the fat body and pericardial cells, inducing cell death. Bees from the FG2 group showed disarranged oenocytes, peripheral vacuolization, and pyknotic nuclei of pericardial cells, but the cytoarchitecture was not compromised as observed in FG1. Additionally, immune system cells were observed through the fat body in the FG1 group. Bees exposed to FG3 demonstrated only oenocytes vacuolization. A significant decrease in the oenocyte’s surface area for bees exposed to all pyraclostrobin concentrations was observed compared to the CTL and CAC groups. The bees from the FG1 and FG2 treatment groups presented a reduced surface area of pericardial cells compared to the controls and the FG3 group. This study highlighted the harmful effects of fungicide pyraclostrobin concentrations at the individual bee cellular level, potentially harming the colony level on continuous exposure.