Keith N. Slessor

Pheromone Communication in the Honeybee (Apis mellifera L.)

Recent studies have demonstrated a remarkable and unexpected complexity in social insect pheromone communication, particularly for honeybees (Apis mellifera L.). The intricate interactions characteristic of social insects demand a complex language, based on specialized chemical signals that provide a syntax that is deeper in complexity and richer in nuance than previously imagined. Here, we discuss this rapidly evolving field for honeybees, the only social insect for which any primer pheromones have been identified. Novel research has demonstrated the importance of complexity, synergy, context, and dose, mediated through spatial and temporal pheromone distribution, and has revealed an unprecedented wealth of identified semiochemicals and functions. These new results demand fresh terminology, and we propose adding “colony pheromone” and “passenger pheromone” to the current terms sociochemical, releaser, and primer pheromone to better encompass our growing understanding of chemical communication in social insects.

The effect of queen pheromones on worker honey bee ovary development

We report results that address a long-standing controversy in honey bee biology, the identity of the queen-produced compounds that inhibit worker honey bee ovary development. As the honey bee is the only organism for which identities have been proposed for any pheromone that regulates reproduction, the resolution of its identity is of broad significance. We examined the effects of synthetic honey bee queen mandibular pheromone (QMP), four newly identified queen retinue pheromone components, and whole-queen extracts on the ovary development of caged worker bees. The newly identified compounds did not inhibit worker ovary development alone, nor did they improve the efficacy of QMP when applied in combination. QMP was as effective as queen extracts at ovary regulation. Caged workers in the QMP and queen extract treatments had better developed ovaries than did workers remaining in queenright colonies. We conclude that QMP is responsible for the ovary-regulating pheromonal capability of queens from European-derived Apis mellifera subspecies.

Synthesis of monosubstituted cyclohexaamyloses

Abstract Eight crystalline, monosubstituted derivatives of cyclohexaamylose have been prepared. They are specifically substituted at C-6 of one of the α- D -glucopyranosyl residues of cyclohexaamylose. 6-O-p-Toluenesulphonyl-cyclohexaamylose was prepared from cyclohexaamylose and purified on a column of activated charcoal. 6-Azido-6-deoxy-, 6-chloro-6-deoxy-, 6-bromo-6-deoxy-, and 6-deoxy-6-iodo-cyclohexaamylose were obtained by nucleophilic displacements of the sulphonate group of the monotosyl-cyclohexaamylose. The monoazido and monoiodo derivatives were reduced to 6-amino-6-deoxy- and 6-deoxy-cyclohexaamylose respectively. 6-O-Trityl-cyclohexaamylose was also prepared from cyclohexaamylose.

Production and transmission of honey bee queen (Apis mellifera L.) mandibular gland pheromone

SummaryThe social cohesiveness of eusocial insect colonies is maintained primarily through the utilization of pheromones. In this study we quantitatively elucidated the production, secretion, and transmission of 9-keto2(E)-decenoic acid (9-ODA), one of the components of the mandibular gland pheromone of the honey bee queen Apis mellifera; this is the only identified primer pheromone complex in the eusocial insects. Mated queens produce 12–400 μg of 9-ODA/day, or between 10% and 170% the average amount found in the glands at any one time. Approximately 0.5 μg of 9-ODA is maintained on the body surface of queens by an equilibrium between exudation, internalization, tracking on the comb, and removal by workers. Retinue bees, attending the queen, remove the greatest amount, although the role of the wax as both a sink and a medium for pheromone transfer has been previously underestimated. Only about 1 in 10 retinue workers pick up substantial quantities of pheromone while attending the queen and, within seconds, most of the acquired 9-ODA is found externally on the abdomen, or in the gut. These attendants, also called messenger bees, transfer 9-ODA to other workers, mostly through direct contacts, but also via the wax. A model evaluating the pathways and relative quantities of 9-ODA transferred throughout the nest is presented. As well as being important for a basic understanding of the system, the results have implications for the proper design and use of pheromones in bee management.

Queen pheromone modulates brain dopamine function in worker honey bees

Honey bee queens produce a sophisticated array of chemical signals (pheromones) that influence both the behavior and physiology of their nest mates. Most striking are the effects of queen mandibular pheromone (QMP), a chemical blend that induces young workers to feed and groom the queen and primes bees to perform colony-related tasks. But how does this pheromone operate at the cellular level? This study reveals that QMP has profound effects on dopamine pathways in the brain, pathways that play a central role in behavioral regulation and motor control. In young worker bees, dopamine levels, levels of dopamine receptor gene expression, and cellular responses to this amine are all affected by QMP. We identify homovanillyl alcohol as a key contributor to these effects and provide evidence linking QMP-induced changes in the brain to changes at a behavioral level. This study offers exciting insights into the mechanisms through which QMP operates and a deeper understanding of the queens ability to regulate the behavior of her offspring.

Caste-Selective Pheromone Biosynthesis in Honeybees

Queen and worker honeybees (Apis mellifera L.) produce a caste-related blend of functionalized 8- and 10-carbon fatty acids in their mandibular glands. The biological functions of these compounds match the queens reproductive and the workers nonreproductive roles in the colony. Studies with deuterated substrates revealed that the biosynthesis of these acids begins with stearic acid, which is hydroxylated at the 17th or 18th position. The 18-carbon hydroxy acid chains are shortened, and the resulting 10-carbon hydroxy acids are oxidized in a caste-selective manner, thereby determining many of the functional differences between queens and workers.

Species- and caste-determined mandibular gland signals in honeybees (Apis)

Queens and workers of five honeybee species (Apis melliferaA. ceranaA. dorsataA. floreaand A. andreniformis) were analyzed for their mandibular gland components. In A. melliferathe queen mandibular pheromone consists of 9-hydroxy- and 9-keto-2(E)-decenoic acids. (9-HDA and ODA), methyl p-hydroxybenzoate (HOB), and 4-hydroxy-3-methoxyphenyl-ethanol (HVA), and is responsible for retinue attraction, among other functions. In retinue bioassays with workers of A. cerana (whose queens lack HVA), ODA, 9-HDA, and HOB were sufficient to elicit maximal retinue behavior. This suggests that the known queen mandibular pheromone components detected in mandibular glands of A. cerana queens constitute the functional queen mandibular pheromone in this species. Both castes of A. mellifera produce 10- and 8-carbon acids that are functionalized at the last position in the chain, and these are the predominant compounds found in worker mandibular glands. Workers of the other species also had these compounds, along with 9-HDA and ODA that are normally not present in A. mellifera worker glands. Queens and workers of each species had a unique combination of mandibular compounds. The aromatic compounds were characteristic of queens from the cavity-nesting speciesA. mellifera (HOB and HVA) and A. cerana (HOB). These two species also had more pronounced differences in the mandibular blends of queens and workers than the open-nesting speciesA. dorsataA. floreaand A. andreniformis. Our results indicate that the more derived cavity-nesting species of Apis have evolved greater caste-specific differences between queens and workers and a higher number of queen pheromone components, compared to the open-nesting species.

Inter- and intrapopulation variation of the pheromone, ipsdienol produced by male pine engravers,Ips pini (Say) (Coleoptera: Scolytidae)

We determined the chirality of ipsdienol in individual male pine engravers,Ips pini (Say), from New York, California, and two localities in British Columbia (BC). Both quantity and chirality of ipsdienol varied significantly between and within populations ofI. pini. Beetles from California and southeastern BC produced primarily (R)-(−)-ipsdienol with mean ratios of (S)-(+) : (R)-(−) of 9 : 91 and 11 : 89, respectively, while beetles from New York produced primarily (S)-(+)-ipsdienol with a mean (S)-(+) : (R)-(−) ratio of 57 : 43. A population from southwestern BC was unlike any other known western population, producing primarily (S)-(+)-ipsdienol with a mean (S)-(+) : (R)-(−) ratio of 66 : 34. In contrast to the unimodal chirality profiles for ipsdienol production in populations from California and southeastern BC, the profiles of the populations from southwestern BC and New York were bimodal, with a common mode at approximately 44 : 56 (S)-(+) : (R)-(−). Bimodality in the profiles of ipsdienol chirality in two populations ofI. pini and remarkably high levels of intrapopulation variation in pheromone chirality in all four populations suggest that evolutionary change in pheromone channels of communication could occur, possibly in response to artificial selection pressures such as mass trapping.

Determination of chirality of alcohol or latent alcohol semiochemicals in individual insects

A method is described for determining the enantiomeric composition of chiral alcohols, lactones, and hydroxy acids in quantities ranging from 25 ng to 10 μg. Derivatization of the substance with chirally pure acetyl lactate, followed by splitless capillary gas chromatography, enables enantiomeric determinations to be made within 1–3% of the actual value. This technique was applied in the determination of semiochemical inIps pini (Say),Apis mellifera (L.), andCryptolestes ferrugineus (Stephens). The results indicate that considerable variability exists within populations of some insects in the composition of their chiral semiochemicals, whereas others produce substances of constant composition.

Enantiomer-based specificity in pheromone communication by two sympatric Gnathotrichus species (Coleoptera: Scolytidae).

The aggregation pheromone ofGnathotrichus retusus was isolated and identified as (S)-(+)-sulcatol (6-methyl-5-hepten-2-ol). In laboratory and field experiments,G. retusus responded to (S)-(+)-sulcatol, but not to (±)-sulcatol, which was attractive to the sympatric species,G. sulcatus. G. sulcatus did not respond to optically pure (S)-(+)-sulcatol, but began to respond when ⩾ 1% (R)-(−)-sulcatol was present in an enantiomeric mixture.