Abstract
Insect antennae are important mechanosensory and chemosensory organs. Insect appendages, such as antennae, are encased in a cuticular exoskeleton and are thought to bend only between segments or subsegments where the cuticle is thinner, more flexible, or bent into a fold. There is a growing appreciation of the dominating influence of folds in the mechanical behavior of a structure, and the bending of cricket antennae was considered in this context. Antennae will bend or deflect in response to forces, and the resulting bending behavior will affect the sensory input of the antennae. In some cricket antennae, such as in those of Acheta domesticus, there are a large number (>100) of subsegments (flagellomeres) that vary in their length. We evaluated whether these antennae bend only at the joints between flagellomeres, which has always been assumed but not tested. In addition we questioned whether an antenna undergoes a length change as it bends, which would result from some patterns of joint deformation. Measurements using light microscopy and SEM were conducted on both male and female adult crickets (Acheta domesticus) with bending in four different directions: dorsal, ventral, medial, and lateral. Bending occurred only at the joints between flagellomeres, and antennae shortened a comparable amount during bending, regardless of sex or bending direction. The cuticular folds separating antennal flagellomeres are not very deep, and therefore as an antenna bends, the convex side (in tension) does not have a lot of slack cuticle to “unfold” and does not lengthen during bending. Simultaneously on the other side of the antenna, on the concave side in compression, there is an increasing overlap in the folded cuticle of the joints during bending. Antennal shortening during bending would prevent stretching of antennal nerves and may promote hemolymph exchange between the antenna and head.
Highlights
Arthopods are encased in an exoskeleton made of cuticle
The mechanical properties of insect antennae are determined in part by the pattern of folds in the cuticle
Applications include design of deployable structures such as airbags, solar sails, and foldable maps, as well as development of lightweight but strong materials such as foams (Heimbs et al, 2009). Some of these applications have been inspired by the study of biological folding structures such as insect wings (Haas and Wootton, 1996; Haas et al, 2000) and tree leaves (Kobayashi et al, 1998, 1999)
Summary
Arthopods are encased in an exoskeleton made of cuticle. Flexible joints are necessary to allow relative movement between stiff parts of an exoskeleton. In insects (and other arthropods), a joint may be formed from thinner or more flexible cuticle (Hepburn and Chandler, 1976), usually associated with a fold (invagination) in the cuticle (Snodgrass, 1935). A planar fold (Figure 1A) will tend to act like a simple hinge joint, allowing rotation at this localized area of lower stiffness (Winder et al, 2009). A planar fold may wrap around a cylindrical appendage, allowing bending in any direction at the joint formed by this cylindrical fold (Figure 1B)
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