Exposure to a sublethal concentration of imidacloprid and the side effects on target and nontarget organs of Apis mellifera (Hymenoptera, Apidae)

Abstract

The use of insecticides has become increasingly frequent, and studies indicate that these compounds are involved in the intoxication of bees. Imidacloprid is a widely used neonicotinoid; thus, we have highlighted the importance of assessing its oral toxicity to Africanized bees and used transmission electron microscopy to investigate the sublethal effects in the brain, the target organ, and the midgut, responsible for the digestion/absorption of food. In addition, the distribution of proteins involved in important biological processes in the brain were evaluated on the 1st day of exposure by MALDI-imaging analysis. Bioassays were performed to determine the Median Lethal Concentration (LC) of imidacloprid to bees, and the value obtained was 1.4651 ng imidacloprid/μL diet. Based on this result, the sublethal concentration to be administered at 1, 4 and 8 days was established as a hundredth (1/100) of the LC. The results obtained from the ultrastructural analysis showed alterations in the midgut cells of bees as nuclear and mitochondrial damage and an increase of vacuoles. The insecticide caused spacing among the Kenyon cells in the mushroom bodies, chromatin condensation and loss of mitochondrial cristae. The MALDI-imaging analysis showed an increase in the expression of such proteins as vascular endothelial growth factor receptor, amyloid protein precursor and protein kinase C, which are related to oxygen supply, neuronal degeneration and memory/learning, and a decrease in the expression of the nicotinic acetylcholine receptor alpha 1, which is fundamental to the synapses. These alterations demonstrated that imidacloprid could compromise the viability of the midgut epithelium, as well as inhibiting important cognitive processes in individuals, and may be reflected in losses of the colony.

Neonicotinoid-containing insecticide disruption of growth, locomotion, and fertility in Caenorhabditis elegans

“…A similar effect was observed in honeybees exposed to imidacloprid [47]. The authors attributed this swelling to larger intercellular spaces within neurons present in exposed honeybees, likely due to damage in cell-cell contact resulting from alterations in the cytoskeleton.…”

Transcriptomic analysis to elucidate the response of honeybees (Hymenoptera: Apidae) to amitraz treatment

“…In our study, up-regulation of two genes (LOC113219 380 and LOC113219382) of Platelet activation pathway after exposure to amitraz (P <0.01), indicating that amitraz might influence the honeybees immunity. Previous study indicated that imidacloprid was involved in the intoxication of honeybees, it could compromise the viability of the midgut epithelium and affected protein digestion and absorption [40]. Comparison of transcriptome profiling between HearNPV-infected and control healthy Helicoverpa armigera larvae during an early stage post-inoculation, KEGG analysis indicated an enrichment of Volcano plot of differentially expressed genes in honeybees exposed to 9.4 mg/L of amitraz for 10 days.…”

MALDI‐imaging analyses of honeybee brains exposed to a neonicotinoid insecticide

“…A sublethal concentration of imidacloprid (Imidacloprid Pestanal – Sigma Aldrich) was added to the diet (aqueous solution of 50% sucrose) of the group exposed to the insecticide based on the LC 50 value (1.4651 ng imidacloprid µL −1 diet). An acetonic solution (15%) of imidacloprid was added to the mother solution and a dilution cascade was made so that the working solution had a final concentration proportional to a sublethal concentration 100 times lower than the LC 50 (LC 50/100 : 0.014651 ng imidacloprid µL −1 diet).…”