Male Labial Gland Research Articles

Male scent-marking pheromone of Bombus ardens ardens (Hymenoptera; Apidae) attracts both conspecific queens and males.

To explore the role of the volatiles emitted from male labial gland (LG) of the bumblebee Bombus ardens ardens, we investigated the responses of virgin queens and males to volatiles using a gas chromatography-electroantennographic detector (GC-EAD) system and Y-tube olfactometer. GC-EAD analysis revealed that citronellol, the main compound detected in the male LG, caused clear electrophysiological responses in the antennae of B. a. ardens virgin queens and males although two minor compounds elicited antennal responses when applied in a high concentration. Behavioral tests using a Y-tube olfactometer showed that queens and males were significantly attracted to both LG extracts and citronellol more than to the solvent alone. This is the first study to demonstrate that citronellol as a major compound of male scent-marking pheromone in B. a. ardens functions as a sex attractant for queens. The results also suggest that this compound has another function as a trail marker used by males.

Exploring complex pheromone biosynthetic processes in the bumblebee male labial gland by RNA sequencing.

Male marking pheromones (MPs) are used by the majority of bumblebee species (Hymenoptera: Apidae), including a commercially important greenhouse pollinator, the buff-tailed bumblebee (Bombus terrestris), to attract conspecific females. MP biosynthetic processes in the cephalic part of the bumblebee male labial gland (LG) are of extraordinary complexity, involving enzymes of fatty acid and isoprenoid biosynthesis, which jointly produce more than 50 compounds. We employed a differential transcriptomic approach to identify candidate genes involved in MP biosynthesis by sequencing Bombus terrestris LG and fat body (FB) transcriptomes. We identified 12454 abundantly expressed gene products (reads per kilobase of exon model per million mapped reads value >1) that had significant hits in the GenBank nonredundant database. Of these, 876 were upregulated in the LG (>4-fold difference). We identified more than 140 candidate genes potentially involved in MP biosynthesis, including esterases, fatty acid reductases, lipases, enzymes involved in limited fatty acid chain shortening, neuropeptide receptors and enzymes involved in biosynthesis of triacylglycerols, isoprenoids and fatty acids. For selected candidates, we confirmed their abundant expression in LG using quantitative real-time reverse transcription-PCR (qRT-PCR). Our study shows that the Bombus terrestris LG transcriptome reflects both fatty acid and isoprenoid MP biosynthetic processes and identifies rational gene targets for future studies to disentangle the molecular basis of MP biosynthesis. Additionally, LG and FB transcriptomes enrich the available transcriptomic resources for Bombus terrestris.

Male labial gland secretions as species recognition signals in species of Bombus

Abstract Spring queens of Bombus cryptarum from Europe, Bombus burjaeticus from the Russian Transbaikal region and Bombus moderatus from North America were collected at different localities to grow artificial colonies and obtain fresh males. Furthermore, males of Bombus florilegus , B. moderatus , Bombus magnus and Bombus occidentalis were collected in the field. Cephalic labial gland secretions of 29 specimens from these different taxa were analysed by gas chromatography/mass spectrometry (GC/MS). About 50 compounds were identified, including a mixture of straight-chain fatty acid derivatives (alkenoles, acids, acetates and esters), and the usual pattern of saturated and unsaturated hydrocarbons C 21 –C 29 . The secretions of all specimens investigated were very similar: ethyl dodecanoate was identified as the main component (90–97% peak area). Since the sum of percentage peak areas for the hydrocarbons amounted up to 3–6%, most of the remaining compounds (8 alkenoles, 6 acids, 6 acetates and 20 esters) could only be detected at very low levels ( B. florilegus , each taxon had a sympatric bumblebee taxon that also used ethyl dodecanoate as the main component: B. magnus , sympatric with B. cryptarum in Europe, Bombus patagiatus , sympatric with B. burjaeticus in the Russian Transbaikal and B. occidentalis , sympatric with B. moderatus in North America. Male cephalic labial gland secretions of 20 specimens from these sympatric taxa were also investigated to see how far their pattern of compounds differed from that of the cryptarum complex taxa ( cryptarum – burjaeticus – florilegus – moderatus ). Besides some quantitative differences in ethyl dodecanoate and ethyl octadec-9-enoate, the occurrence of octadeca-9,12-dien-1-ol, octadeca-9,12,15-trien-1-ol and octadec-11-en-1-ol was an essential qualitative difference that separated the labial gland secretions of B. magnus , B. patagiatus and B. occidentalis from those of their sympatric counterparts. A principal component analysis confirmed this separation. Due to their low variability and differences in pattern of compounds compared to those of closely related sympatric bumblebees, the labial gland secretions of B. cryptarum , B. burjaeticus, B. florilegus and B. moderatus distributed across Europe, the Russian Far East and North America are very well suited to function as ‘species recognition signal’. The taxonomic consequences for the cryptarum complex taxa and their relationship to Bombus albocinctus from the Russian Far East are discussed in context of recent genetic investigations.

Comparison of Age-dependent Quantitative Changes in the Male Labial Gland Secretion of Bombus Terrestris and Bombus Lucorum

Age-related changes of antennal-active components of male labial gland extracts were studied in two closely related bumblebee species, Bombus terrestris and B. lucorum. In B. terrestris, compounds eliciting electroantennogram (EAG) responses of virgin queens were ethyl dodecanoate, 2,3-dihydrofarnesal, 2,3-dihydrofarnesol, hexadecan-1-ol, octadeca-9,12,15-trien-1-ol, and geranylcitronellol. Compounds that elicited EAG responses from queens of B. lucorum were ethyl dodecanoate, ethyl tetradec-7-enoate, ethyl tetradec-9-enoate, ethyl hexadec-9-enoate, hexadecan-1-ol, hexadec-7-enal, octadeca-9,12-dien-1-ol, octadeca-9,12,15-trien-1-ol, and octadecan-1-ol. Quantities of these compounds in the labial glands changed significantly over the lifetime of the respective males of the two species. In both species, concentrations of the respective compounds reached their maximum within seven days after eclosion. Subsequently, a rapid decrease in the amount of EAG-active compounds occurred in B. terrestris, whereas in B. lucorum the amount of active compounds stayed approximately constant or decreased at a slow rate. Microscopy showed that in B. terrestris secretory cells of the labial glands undergo apoptosis from the fifth to the tenth day of life, whilst in B. lucorum labial gland cells remain unchanged throughout the life of the males.

Age-dependent changes in structure and function of the male labial gland in Bombus terrestris

The cephalic region of the labial gland in the buff-tailed bumblebee, Bombus terrestris, consists of numerous acini (formed by associated secretory cells and a central lumen) and connecting ducts. Age-dependent changes in secretion production (both qualitative and quantitative) are associated with changes in the amount of rough endoplasmic reticulum (RER), Golgi apparatus, and smooth endoplasmic reticulum (SER). The main secretory organelle is RER in the youngest individuals (pharate, and less-than-a-day old males), Golgi apparatus in 1-day-old males, and SER in males older than 2 days. Secretory cell death starts at 5 days of age, with maximal longevity to 10 days. Pheromone production starts immediately after eclosion, with pheromone quantities increasing until day 7. 2,3-Dihydrofarnesol, the main component of the male-marking pheromone, appears in 1-day-old male glands, and reaches a maximum at 7 days of age, when its presence in the gland starts to decrease gradually. Older glands contain compounds not present in young ones. Variation in pheromone quantity and composition are reflected sensitively in the response of the queen antennae. Though queen antennae responded to gland extracts of all ages examined, maximum sensitivity was observed in response to extracts of glands 2–10 days old, while extracts of older glands gradually lose their effectiveness. Both major and minor components of the labial gland secretion extract elicited queen antennal responses suggesting that the pheromone is a multicomponent blend. Age-dependent changes in pheromone production, accumulation and tuning of pheromone activity are all synchronized approximately with male flight from the hive.

Abgrenzung der Hummel-Arten Bombus cryptarum und B lucorum mittels männlicher Labialdrüsen-Sekrete und morphologischer Merkmale (Hymenoptera, Apidae)

Three taxa of the subgenus Terrestribombus Vogt 1911 [genus Bombus Linnaeus 1758] have been reared in the laboratory and assigned by the main component (MC) of the male labial gland secretions to the species terrestris Linnaeus 1758 (MC = 2,3-Dihydrofarnesol), lucorum Von Linne 1761 (MC = Myristoleic acid ethyl ester) and cryptarum Fabricius 1775 (MC = Lauric acid ethyl ester). Individuals of terrestris can be identified by proboscis-length, individuals of lucorum and cryptarum by the Rf-values of Phosphoglucomutase on PAGE-gel. Coloration and boundary of the collare at the edge of the pronotolobus of queens are reliable characters to discriminate cryptarum and lucorum. 39 compounds including mainly hydrocarbons, alcohols and esters are identified from the male labial glands of cryptarum.