Many animals, but especially insects, monitor their environment through the perception of chemical signals and cues, which can provide vital information, including the location of food resources, oviposition sites or reproductive partners. This form of communication differs from other modalities in a crucial way: detection of the signal or cue requires a physical interaction between the odorant molecule and the odour receptor. The receptors used to detect these odours are mostly located on sensilla that are supported by the antennae. The diverse morphologies of insect antennae and the sensilla they support are both astonishing and puzzling: what selective pressures are responsible for these morphologically different solutions to the same problem — to perceive signals and cues? Here, I discuss the natural and sexual selection pressures that act on the number of sensilla supported by the antennae. These pressures are likely balanced against the costs of producing and receiving chemical signals. While these questions address fundamental issues, there are more practical insights: air pollution dramatically compromises the capacity of insects to detect odours, and so perhaps contributes to their global population decline.
Natural and sexual selection pressures influencing chemical sensory morphology in insects