A Gland of Many Uses: a Diversity of Compounds in the Labial Glands of the Bumble Bee Bombus impatiens Suggests Multiple Signaling Functions.

Margarita Orlova,Etya Amsalem,Abraham Hefetz,Jocelyn G Millar,Gabriel Villar

doi:10.1007/s10886-022-01348-4

Abstract

Communication in social insect colonies depends on signals accurately reflecting the identity and physiological state of the individuals. Such information is coded by the products of multiple exocrine glands, and the resulting blends reflect the species, sex, caste, age, task, reproductive status, and health of an individual, and may also contain caste-specific pheromones regulating the behavior and physiology of other individuals. Here we examined the composition of labial gland secretions in females of the bumble bee Bombus impatiens, of different castes, social condition, age, mating status, and ovarian activation. We show that active queens, gynes, and workers each produce caste-specific compounds that may serve different communicative functions. The composition and amounts of wax esters, mostly octyl esters produced by active queens, differed significantly between castes, mating, and social conditions, suggesting a social signaling role. Farnesyl esters were predominant in gynes and peaked at optimal mating age (6-10days), suggesting their possible roles as sex pheromone components. Reproductive status of females and age across castes was reflected by the ratio between short- and long-chain hydrocarbons, suggesting that these compounds may serve as fertility signals. Our findings overall suggest that the labial gland composition in B. impatiens reflects different facets of female physiology. While further bioassays are required to determine the functions of these compounds, they are likely to have important roles in communication between individuals.

Highlights

Insect societies rely on chemical signaling for regulating diverse activities ranging from foraging to reproduction, and the outcome of communication depends heavily on how accurately the signals reflect the identity and physiological state of the individuals
Our analysis of the cephalic labial gland secretions revealed a great diversity of compounds representing a number of different chemical classes
Some of these differences, such as the abundance of terpenoids in gynes and the octyl esters in queens, parallel those found in other secretions of B. impatiens and B. terrestris (Amsalem et al 2014; Amsalem et al 2009; Derstine et al 2021)

Summary

Introduction

Insect societies rely on chemical signaling for regulating diverse activities ranging from foraging to reproduction, and the outcome of communication depends heavily on how accurately the signals reflect the identity and physiological state of the individuals. Some exocrine glands are specific to certain taxa, whereas others are shared across taxa These ubiquitous glands in insects are useful tools to study the emergence of new signaling functions across species and levels of social organization. The labial glands have thoracic and cephalic compartments, located, respectively, in the thorax and the head (Poiani and Cruz-Landim 2009) These two compartments have the same origin and likely share the same secretion in species that have a salivary pouch at the intersection of the compartments (Bombus and Meliponinae genera) (Poiani and Cruz-Landim 2010), making this gland suitable for examining functions associated with social signaling across insect species. Some species (e.g., Apis mellifera) lack this pouch and it is still debatable whether the secretion is the same (Katzav-Gozansky et al 2001) or different (Poiani and Cruz-Landim 2010) between the two compartments, but the cephalic labial glands are well-developed in eusocial species of the subfamily Apinae in which the secretion is assumed to be associated with social roles (Poiani and Cruz-Landim 2010)

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Conclusion