The diversity, evolution, and development of setal morphologies in bumble bees (Hymenoptera: Apidae: Bombus spp.)

Abstract

Bumble bees are characterized by their thick setal pile that imparts aposematic color patterns often used for species-level identification. Like all bees, the single-celled setae of bumble bees are branched, an innovation thought important for pollen collection. To date no studies have quantified the types of setal morphologies and their distribution on these bees, information that can facilitate understanding of their adaptive ecological function. This study defines several major setal morphotypes in the common eastern bumble bee Bombus impatiens Cresson, revealing these setal types differ by location across the body. The positions of these types of setae are similar across individuals, castes, and sexes within species. We analyzed the distribution of the two most common setal types (plumose and spinulate) across the body dorsum of half of the described bumble bee species. This revealed consistently high density of plumose (long-branched) setae across bumble bees on the head and mesosoma, but considerable variation in the amount of metasomal plumosity. Variation on the metasoma shows strong phylogenetic signal at subgeneric and smaller group levels, making it a useful trait for species delimitation research, and plumosity has increased from early Bombus ancestors. The distribution of these setal types suggests these setae may serve several functions, including pollen-collecting and thermoregulatory roles, and probable mechanosensory functions. This study further examines how and when setae of the pile develop, evidence for mechanosensory function, and the timing of pigmentation as a foundation for future genetic and developmental research in these bees.

Lepidopteran scale cells derive from sensory organ precursors through a canonical lineage

“…From a macroevolutionary perspective, our data validates the serial homology of lepidopteran scales with dipteran sensory bristles. However, it is unclear if these represent a case of orthology, because scales may have instead evolved from a non-sensory serial homologue that pre-existed in a common ancestor, akin to the ornamental setae and scales found in bumblebees and mosquitoes (Djokic et al, 2020; Hines et al, 2022).…”

Cuticular hydrocarbon profiles of Himalayan bumble bees (Hymenoptera:BombusLatreille) are species-specific and show local and elevation related variation

“…Due to their importance as pollinators of many flowering plants, bumble bees and other wild bees became a model system to better understand their vulnerability and resilience against climate changes (Soroye et al 2020;Maebe et al 2021;Warrit et al 2023). Possible mechanisms of adaptation include, for example, pilosity (Hines et al 2022), cuticular hydrocarbons (Maihoff et al 2023), temperature tolerance (Pimsler et al 2020;Martinet et al 2021), respiratory and neural systems (Jackson et al, 2020).…”