Abstract
Honeybees secrete 2-heptanone (2-H) from their mandibular glands when they bite. Researchers have identified several possible functions: 2-H could act as an alarm pheromone to recruit guards and soldiers, it could act as a chemical marker, or it could have some other function. The actual role of 2-H in honeybee behaviour remains unresolved. In this study, we show that 2-H acts as an anaesthetic in small arthropods, such as wax moth larva (WML) and Varroa mites, which are paralysed after a honeybee bite. We demonstrated that honeybee mandibles can penetrate the cuticle of WML, introducing less than one nanolitre of 2-H into the WML open circulatory system and causing instantaneous anaesthetization that lasts for a few minutes. The first indication that 2-H acts as a local anaesthetic was that its effect on larval response, inhibition and recovery is very similar to that of lidocaine. We compared the inhibitory effects of 2-H and lidocaine on voltage-gated sodium channels. Although both compounds blocked the hNav1.6 and hNav1.2 channels, lidocaine was slightly more effective, 2.82 times, on hNav.6. In contrast, when the two compounds were tested using an ex vivo preparation–the isolated rat sciatic nerve–the function of the two compounds was so similar that we were able to definitively classify 2-H as a local anaesthetic. Using the same method, we showed that 2-H has the fastest inhibitory effect of all alkyl-ketones tested, including the isomers 3- and 4-heptanone. This suggests that natural selection may have favoured 2-H over other, similar compounds because of the associated fitness advantages it confers. Our results reveal a previously unknown role of 2-H in honeybee defensive behaviour and due to its minor neurotoxicity show potential for developing a new local anaesthetic from a natural product, which could be used in human and veterinary medicine.
Highlights
Does 2-H Function as an Alarm Pheromone? We first tested the dominant hypothesis that honeybees secrete
Though 2-H is highly volatile and detectable by honeybees at low concentrations (4.049 mg/mL; molar fraction = 6.19), the absence of any reaction during our research or during experiments where 2-H was delivered to the hive entrance via air pumping [10] suggests that it is unlikely that 2-H functions in pheromonal ‘‘emission-reception’’ transmission from a guard honeybee to the colony
The present study revealed that in addition to injecting venom via a sting, honeybees can use 2-H for defence, to paralyse invaders that are too small to sting. 2-H is produced in the mandibular glands, released by the mandible pore of a reservoir and through the groove flows at the sharp edge of mandibles
Summary
The purpose of this paper is to provide an in-depth investigation of the possible anaesthetic properties of 2-H during honeybee defense and to examine whether 2-H acts as a local anaesthetic on the mammalian peripheral nervous system
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