Monoterpenoid‐based preparations in beehives affect learning, memory, and gene expression in the bee brain

Abstract

Bees are exposed in their environment to contaminants that can weaken the colony and contribute to bee declines. Monoterpenoid-based preparations can be introduced into hives to control the parasitic mite Varroa destructor. The long-term effects of monoterpenoids are poorly investigated. Olfactory conditioning of the proboscis extension reflex (PER) has been used to evaluate the impact of stressors on cognitive functions of the honeybee such as learning and memory. The authors tested the PER to odorants on bees after exposure to monoterpenoids in hives. Octopamine receptors, transient receptor potential-like (TRPL), and γ-aminobutyric acid channels are thought to play a critical role in the memory of food experience. Gene expression levels of Amoa1, Rdl, and trpl were evaluated in parallel in the bee brain because these genes code for the cellular targets of monoterpenoids and some pesticides and neural circuits of memory require their expression. The miticide impaired the PER to odors in the 3 wk following treatment. Short-term and long-term olfactory memories were improved months after introduction of the monoterpenoids into the beehives. Chronic exposure to the miticide had significant effects on Amoa1, Rdl, and trpl gene expressions and modified seasonal changes in the expression of these genes in the brain. The decrease of expression of these genes in winter could partly explain the improvement of memory. The present study has led to new insights into alternative treatments, especially on their effects on memory and expression of selected genes involved in this cognitive function. Environ Toxicol Chem 2017;36:337-345. © 2016 SETAC.

The miticide thymol in combination with trace levels of the neonicotinoid imidacloprid reduces visual learning performance in honey bees (Apis mellifera)

“…learning performance of bees treated with thymol and/or imidacloprid Here, we focused on thymol as a miticide because of its demonstrated effects on olfactory memory and phototaxis (Carayon et al 2014;Alayrangues et al 2016;Bonnafé et al 2017). Bees were sourced from sixteen colonies used in Colin et al (2019a).…”

“…GABA is an important neurotransmitter for both mites and insects, and hence there are legitimate concerns that thymol also affects honey bees. For example, Apilife Var®, a commercial formulation of thymol, eucalyptus oil, camphor, and levomenthol, is known to impair olfactory memory and phototactic response in bees shortly after its introduction in the hive (Carayon et al 2014;Alayrangues et al 2016;Bonnafé et al 2017). In this study, we compared the effects of two miticide treatments: the Apiguard® formulation of thymol and the Apistan® formulation of tau-fluvalinate on honey bee visual learning.…”

“…In our first experiment, we compared visual learning and memory performance of bees exposed to commercial miticide formulations of tau-fluvalinate and thymol miticides and untreated controls. In our second experiment, we chose to further investigate the effect of thymol, because of recent reports of its effects on olfactory memory and bee colonies (Tihelka 2018;Colin et al 2019a;Colin et al 2019c;Bonnafé et al 2017) and compared visual learning performance of bees exposed to either thymol, a trace level of imidacloprid, or both substances together and untreated controls.…”

Impact of Stressors on Honey Bees (Apis mellifera; Hymenoptera: Apidae): Some Guidance for Research Emerge from a Meta-Analysis

“…For example, one hypothesis to explain recurrent weakening of honey bee colonies is that disoriented bees are no longer able to find their way home [12]. Thus, the effect of stressors on bee health is not limited to lethal effects but is also related to behavioral changes [13], impaired cognitive functions and sensory abilities [14,15], and physiological [16], molecular [17] and genetic changes [10]. At present, the effects of pesticides and other stressors on bee health are still poorly understood and are not evaluated by standard regulatory procedures for risk assessment [18].…”

The Effect of Eucalyptol on Nursing Home Residents

“…Inhaled air containing a scent can reach the circulatory system but can also stimulate brain areas directly via receptors in the olfactory epithelium. Once the signals reach the olfactory cortex, release of neurotransmitters and neuropeptides takes place, which results in a marked effect on emotions [3][4][5] . Previous studies by Goto showed that visiting a small indoor garden with 20 pots of chrysanthemums for 15 minutes improved the mood of elderly subjects with dementia 6 .…”