Honey bee (Apis mellifera ligustica) acetylcholinesterase enzyme activity and aversive conditioning following aluminum trichloride exposure

Abstract

Background Aluminum is the third most prevalent element in the earth’s crust. In most conditions, it is tightly bound to form inaccessible compounds, however in low soil pH, the ionized form of aluminum can be taken up by plant roots and distributed throughout the plant tissue. Following this uptake, nectar and pollen concentrations in low soil pH regions can reach nearly 300 mg/kg. Inhibition of acetylcholinesterase (AChE) has been demonstrated following aluminum exposure in mammal and aquatic invertebrate species. In honey bees, behaviors consistent with AChE inhibition have been previously recorded; however, the physiological mechanism has not been tested, nor has aversive conditioning. Results This article presents results of ingested aqueous aluminum chloride exposure on AChE as well as acute exposure effects on aversive conditioning in an Apis mellifera ligustica hive. Contrary to previous findings, AChE activity significantly increased as compared to controls following exposure to 300 mg/L Al3+. In aversive conditioning studies, using an automated shuttlebox, there were time and dose-dependent effects on learning and reduced movement following 75 and 300 mg/L exposures. Conclusions These findings, in comparison to previous studies, suggest that aluminum toxicity in honey bees may depend on exposure period, subspecies, and study metrics. Further studies are encouraged at the moderate-high exposure concentrations as there may be multiple variables that affect toxicity which should be teased apart further.

Preliminary Evidence That Fiji Water Has Protective Effects against Aluminum Toxicity in Honey Bees (Apis mellifera)

“…For the AlCl3 at 300 mg/L concentration groups, these results might be the effect of a similar finding where the 300 mg/L exposure spiked AChE tissue activity compared to other doses (more AChE → less ACh → less movement) [ 9 ]. In comparison, the Fiji 1 group had a significant spike in average rhythmicity levels around 6:00 AM−6:00 PM compared to the other groups who exhibited decreases or no change during that time ( Figure 1 A–D).…”

“…In comparison, Delkash-Roudsari et al [ 29 ] used a 14-day dosing period or until all bees were dead for data collection, which is lower than the 16-day period we used. Like other experiments, we used DI water in our experiment [ 9 , 17 , 18 , 29 , 35 ]. The bees in both our control and experimental solution groups consumed DI water.…”

“…Aluminum is increasing in bioavailability through acidification from carbon emissions and mining practices, which may lead to a higher risk of honey bees being exposed to this metal. Aluminum toxicity has negative impacts on honey bee behavior and physiology, making it difficult for them to perform crucial survival behaviors such as foraging [ 9 , 17 , 18 ]. As a result, it is important for researchers to develop methods that help to minimize the effects of aluminum on honey bees.…”

“…Aluminum toxicity impacts the cholinergic system by altering the enzyme activity of acetylcholinesterase (AChE) in the brain [ 9 , 10 , 11 , 12 ]. Disruption of this system is associated with impairments in motor functioning, learning, and memory [ 13 , 14 , 15 ].…”

“…Since eusocial forager honey bees supply food for the winter stores, choosing poorer resources may impact hive health. Honey bees have also been shown to have altered AChE and dose-dependent behavioral outcomes following exposure to aluminum trichloride [ 9 ].…”