The Bite of the Honeybee: 2-Heptanone Secreted from Honeybee Mandibles during a Bite Acts as a Local Anaesthetic in Insects and Mammals

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.

The defensive response of the honeybee Apis mellifera

“…The emerging larvae feed on wax and hive debris, tunnelling just under the cell caps and feeding on discarded cocoons, thus destroying the combs. Honeybees remove wax moth larvae by biting and dragging them out of the nest (Papachristoforou et al, 2012;Yang et al, 2010). Intruding beetles are usually mauled by several guard bees.…”

“…A pore on the internal face of the mandibles allows this secretion to flow out of the mandibular glands, and a groove directs it towards the sharp edges at the tip of the spatula (Fig. 2B, red) (Papachristoforou et al, 2012;Vallet et al, 1991). Young bees produce very small amounts of 2-heptanone, but as they get older this quantity slowly increases.…”

“…Only one study found that 2-heptanone and IAA had similar efficiency: when presented simultaneously on two moving balls, the bees did not attack either one preferentially (Free and Simpson, 1968). In fact, in some studies, 2-heptanone acts as a repellent or does not elicit any reaction from the guard bees (Butler, 1966;Papachristoforou et al, 2012;Vallet et al, 1991).…”

Local Anaesthetic Properties vs. Neurotoxicity for (+)- and (−)-Carvone: An Ex Vivo Electrophysiological Study

“…This contrasts dramatically with the 83-87% recovery after incubation in carvone-enriched saline for 6-7 min. It also contrasts with the results for lidocaine and 2-heptanone, a natural compound with local anaesthetic action [15]. There was a full recovery of the CAP to 98% after 1 h of incubation in 10.0 mM lidocaine, which remained at this level for 24 h (l " Fig.…”

“…In these experiments, for a better comparison of the neurotoxic effect, an additional natural compound with local anaesthetic properties, 2-heptanone [15], was tested. For data analysis, the amplitude of CAP, measured in Volts, was expressed as a percentage of (i) the last value recorded before the application of the tested compound (for short-term experiments) or (ii) the higher CAP amplitude value recorded throughout the experiment (for long-term experiments), which was considered as 100%.…”