Is the Salivary Gland Associated with Honey Bee Recognition Compounds in Worker Honey Bees (Apis mellifera)?

Abstract

Cuticular hydrocarbons (CHCs) function as recognition compounds with the best evidence coming from social insects such as ants and honey bees. The major exocrine gland involved in hydrocarbon storage in ants is the post-pharyngeal gland (PPG) in the head. It is still not clearly understood where CHCs are stored in the honey bee. The aim of this study was to investigate the hydrocarbons and esters found in five major worker honey bee (Apis mellifera) exocrine glands, at three different developmental stages (newly emerged, nurse, and forager) using a high temperature GC analysis. We found the hypopharyngeal gland contained no hydrocarbons nor esters, and the thoracic salivary and mandibular glands only contained trace amounts of n-alkanes. However, the cephalic salivary gland (CSG) contained the greatest number and highest quantity of hydrocarbons relative to the five other glands with many of the hydrocarbons also found in the Dufour’s gland, but at much lower levels. We discovered a series of oleic acid wax esters that lay beyond the detection of standard GC columns. As a bee’s activities changed, as it ages, the types of compounds detected in the CSG also changed. For example, newly emerged bees have predominately C19-C23n-alkanes, alkenes and methyl-branched compounds, whereas the nurses’ CSG had predominately C31:1 and C33:1 alkene isomers, which are replaced by a series of oleic acid wax esters in foragers. These changes in the CSG were mirrored by corresponding changes in the adults’ CHCs profile. This indicates that the CSG may have a parallel function to the PPG found in ants acting as a major storage gland of CHCs. As the CSG duct opens into the buccal cavity the hydrocarbons can be worked into the comb wax and could help explain the role of comb wax in nestmate recognition experiments.

Relationship Between Hydrocarbon Composition on the Cuticle of Melipona quadrifasciata (Hymenoptera: Apidae) Workers and the Secretion of the Cephalic Salivary Glands

“…However, some epidermal cells that function as tegumental glands are also involved in cuticle hydrocarbon synthesis (Kramer & Wigglesworth, 1950;Abdalla et al, 2003) and such compounds can be fully or partially stored in glands after being released as secretion . The present research showed that hydrocarbons were the major compounds in CSG indicating that the studied gland may be an auxiliary source of cuticle hydrocarbons as observed in A. mellifera (Poiani & Cruz-Landim, 2017;Martin et al, 2018). In ants, the postpharyngeal gland (PPG) contains similar hydrocarbons found on cuticle surface (Bagnères & Morgan, 1991;Kaib et al, 2000).…”

“…Also, it aids to handle resins collected in the field (Santos et al, 2009). In A. mellifera and some Bombus species, the hydrocarbons produced by CSG are also present in the cuticle of workers (Kullenberg et al, 1973;Arnold et al, 1996;Poiani & Cruz-Landim, 2017;Martin et al, 2018). In A. mellifera, CSG may take part as an auxiliary source of cuticular hydrocarbons (Poiani & Cruz-Landim, 2017).…”

The cuticular hydrocarbon profiles of honey bee workers develop via a socially-modulated innate process

“…Based on these studies, it has been hypothesized that, similar to some ant species, the CHC profile of newly eclosed workers represents a ‘blank slate’ (Breed et al, 2004; Lenoir et al, 1999), and that nestmate recognition cues are subsequently acquired by individual workers primarily through the homogenization and transfer of chemicals via direct social interactions and intermediate environmental factors (Breed et al, 2015). Furthermore, it has recently been proposed that the cephalic salivary gland of honey bee workers is functionally analogous to the PPG in ants, and could be involved in the homogenization and transfer of the CHCs between colony members (Martin et al, 2018). However, when and how honey bee chemical nestmate recognition cues mature, and whether CHC homogenization mechanisms play a role in this process have not been directly investigated.…”