Abstract
AbstractThe exoskeleton (cuticle) of insects varies widely in shape, biomechanical properties, and functions, which are inherent to the biological species and developmental stage, besides showing a wealth of architectural specializations and nuances in the different body regions. The morphological pattern of exoskeleton maturation was studied in eusocial and solitary bees, including species of all three eusocial tribes of corbiculate bees as follows: Apini, Meliponini, and Bombini. The results showed striking differences in the rate of cuticle maturation between the solitary bees that leave the nest soon after the adult ecdysis, and the eusocial bees that take longer to leave the colony for foraging activities. There was a clear delay in the post-ecdysial cuticle tanning (melanization and sclerotization) in the eusocial bee species in comparison to the solitary species, suggesting adaptation to sociality and to the protective environment of the colony. Such heterochrony of cuticle maturation seems a conserved ontogenetic trait related to the way of life in corbiculate bees. The data generated a basic framework of exoskeleton maturation in corbiculate bees, under ontogenetic and evolutionary approaches, and give experimental support for further research on adaptation to the colony environment.
Highlights
The cuticular exoskeleton is a multifunctional structure because in addition to the support it provides the insects, it allows locomotion and movements, protects against predators, and prevents desiccation, besides functioning in the mechanical digestion carried out by mouthparts, Exoskeleton differentiation is a remarkable event of insect ontogenesis and occurs through a process known as tanning, meaning the progressive darkening and hardening of the newly-secreted cuticle (Andersen 2005)
Melanization starts in the developing adult cuticle 80 h after pupal cuticle apolysis, approximately (Michelette and Soares 1993)
Forager bees from the eusocial species A. mellifera, F. varia, T. angustula, S. aff. depilis, M. scutellaris, and B. morio showed in a lesser or greater degree, depending on the species, a darker and stiffer cuticular exoskeleton than newly-emerged bees. Such difference was not observed in the solitary bee species (C. analis and T. diversipes) (Figure 1)
Summary
The cuticular exoskeleton is a multifunctional structure because in addition to the support it provides the insects, it allows locomotion and movements, protects against predators, and prevents desiccation, besides functioning in the mechanical digestion carried out by mouthparts, Exoskeleton differentiation is a remarkable event of insect ontogenesis and occurs through a process known as tanning, meaning the progressive darkening (melanization) and hardening (sclerotization) of the newly-secreted cuticle (Andersen 2005). Two basic types of exoskeleton can be identified in the honey bees, the flexible and colorless (unpigmented) larval and pupal exoskeletons, and the rigid (highly sclerotized) and pigmented adult exoskeleton. Melanin pigments are deposited into the adult cuticle, which becomes increasingly sclerotized, as it differentiates. Melanization starts in the developing adult cuticle 80 h after pupal cuticle apolysis, approximately (Michelette and Soares 1993). Apolysis progressively occurs along the anterior–posterior body axis, and adult cuticle deposition and tanning follow this pattern. The abdomen is weakly pigmented and sclerotized until close to the adult ecdysis
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