The Effect of Caste and Reproductive State on the Chemistry of the Cephalic Labial Glands Secretion of Bombus Terrestris

Abstract

The cephalic labial glands are well developed in many bee species. In bumble bee males, they cover most of the head volume, and their secretion is used in marking reproductive territories and attracting virgin queens. In females, however, they are poorly studied. Here, we present chemical analyses of their secretion in queens and workers of Bombus terrestris under various social conditions. The secretion revealed a context-dependent composition with sterile females possessing large amounts of fatty acid dodecyl esters, ranging from dodecyl hexanoate to dodecyl oleate, compared to small amounts in fertile females. Significant reduction in the dodecyl esters also was found in queens at the competition phase, where worker reproduction, aggression, and gyne differentiation occur. The exclusive production of esters by sterile individuals also is typical of Dufour's gland secretion in this species, albeit in this case these are octyl rather than dodecyl esters, and the differences between sterile and fertile individuals are qualitative rather than quantitative. We propose that the labial gland esters provide yet another signal of reproductive inactivity. In virgin queens, it may signal that egg laying is deferred to the next season, while in workers it reinforces the message "I am sterile and out of the reproductive competition". Whether the reduction in dodecyl esters in fertile queens as a function of colony social development is involved in regulating gyne production and the onset of the competition phase is yet to be deciphered.

A conserved class of queen pheromones? Re-evaluating the evidence in bumblebees ( Bombus impatiens )

“…Notably, there was no difference in responses of naive and experienced workers to the high dose of C 23 and C 27. However, C 25 is far more abundant than C 23 and C 27 in B. terrestris [29,30,43], and in B. impatiens too the quantities of C 25 were 3.44 times higher compared with C 27 and only slightly higher (1.1-fold) compared with C 23 (table 1).…”

“…However, as noted above, hydrocarbons seem to be unlikely candidates for 'queen pheromones' because they are so ubiquitous and variable [21]. Indeed, in B. terrestris bumblebees, C 25 is found in high quantities on the cuticular surface and in most exocrine glands of queen and workers, both fertile and non-reproductive [29,30].…”

“…Previous studies indicated that contact with the queen was necessary to reduce worker ovary activation rates [23,24]. Whole body washes can reduce juvenile hormone titres in workers ( juvenile hormone is a gonadotropin in bumblebees [25][26][27]), but the identity of the chemical signals have eluded researchers [27][28][29][30].…”

Identification and Synthesis of Branched Wax‐type Esters, Novel Surface Lipids from the Spider Argyrodes elevatus (Araneae: Theridiidae)

“…The only related compounds from spiders are branched propyl esters with a chain length between C 24 and C 36 , present on the cuticle of another but distantly related theridiid Anelosimus eximius, together with hydrocarbons and other components [14]. Wax esters as carriers of chemical signals have been reported, e. g., in bees and bumblebees [49]. eximus [23].…”

Ultrastructural detection of lipids in the cephalic salivary glands of Apis mellifera and Scaptotrigona postica (Hymenoptera: Apidae) workers

“…This plasticity is observed not only among different species, but also between the sexes and castes of the same species. For example, males of Bombus pratorum (Linnaeus, 1761) and Bombus lapidarius (Linnaeus, 1758) use the CSG secretion to mark flight routes and attract virgin queens (BerGman & BerGström 1997), while females (queens and workers) of Bombus terrestris (Linnaeus, 1758) use CSG as a reproductive status signal (amsaLem et al 2014). The function of the CSG secretion of A. mellifera is not clear, but it has been hypothesized to soften wax during nest construction (HeseLHaus 1922), and to lubricate mouthparts (simpson 1960).…”