Abstract
Simple SummaryThe antennae of insects are multipurpose sensory organs that can detect chemicals, gravity, vibrations, and sound, among others. While such sensors are very specialized and adapted to their specific needs, the way the antenna itself is built has often been considered either uninteresting or unimportant. We used a laser to scan the antenna of the midge Chironomus riparius. Insect cuticle, if illuminated with laser light, reflects autofluorescent light, an emission that has long been known to indicate the material properties of the scanned cuticle sample. Rather than a simple beam-like structure of constant material stiffness, we saw bands of hard and soft material, distributed along the length of the antenna. We were able to computer-simulate the effect of this banded structure on the antenna’s resonant frequency and showed that it allows the beam to vibrate at different frequencies than would be expected only by its shape. This discovery will help us to better understand these animals’ biology and can inspire future biomimetic sensors for detecting sound or vibration.Small-scale bioacoustic sensors, such as antennae in insects, are often considered, biomechanically, to be not much more than the sum of their basic geometric features. Therefore, little is known about the fine structure and material properties of these sensors—even less so about the degree to which the well-known sexual dimorphism of the insect antenna structure affects those properties. By using confocal laser scanning microscopy (CLSM), we determined material composition patterns and estimated distribution of stiffer and softer materials in the antennae of males and females of the non-biting midge Chironomus riparius. Using finite element modelling (FEM), we also have evidence that the differences in composition of these antennae can influence their mechanical responses. This study points to the possibility that modulating the elastic and viscoelastic properties along the length of the antennae can affect resonant characteristics beyond those expected of simple mass-on-a-spring systems—in this case, a simple banded structure can change the antennal frequency sensitivity. This constitutes a simple principle that, now demonstrated in another Dipteran group, could be widespread in insects to improve various passive and active sensory performances.
Highlights
Contrary to mosquitoes, whose bite is a nuisance and a pathway for the transmission of disease, midges receive limited scientific attention
As in the previous study [16], which deployed state-of-the-art confocal laser scanning microscopy (CLSM), the present study presents morphology of the male and female antenna of C. riparius through observation of different autofluorescences of varying cuticle configurations
The flagellum is composed of 11 units, called flagellomeres
Summary
Contrary to mosquitoes, whose bite is a nuisance and a pathway for the transmission of disease, midges receive limited scientific attention. The present study on the intricate antennal structure, especially of the male non-biting midge Chironomus riparius, aims to reveal some adaptations of these animals’ biology. Chironomus riparius is a non-biting midge that, like many mosquitoes, displays swarming behaviour [5,6,7]. Since acoustic communications play an essential role in finding mating partners [5,7,8,9], it is reasonable to expect that there are similarities in the antennal form and properties in species of midges and mosquitoes whose mating behaviour includes swarming. Most neurons in the Johnston’s organ are thought to be involved with acoustic perception, which ones remains a matter for debate [14]
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