Lasers may be a cutting-edge tool for identifying insects, but at the heart of the lidar method is an elegant and centuries-old principle of entomology. Almost every species of flying insect, from moth to midge to mosquito, has a unique wingbeat frequency. A female Culex stigmatosoma mosquito, for instance, might beat its wings at a frequency of 350 hertz, while a male Culex tarsalis might at 550 hertz. Because of these differences, an insect’s wingbeat is like a fingerprint. And in recent years, the study of wingbeat has undergone a renaissance, especially in the field of human health.
Long before lasers or computers, wingbeat was thought of in auditory – even musical – terms. A careful listener could match the buzz of a fly to a key on the piano. That is exactly what Robert Hooke, a natural philosopher, did in the 17th century: “He is able to tell how many strokes a fly makes with her wings (those flies that hum in their flying) by the note that it answers to in musique during their flying,” wrote Samuel Pepys, a British civil servant and friend of Hooke’s.
“The acoustic method makes it possible to observe insects in free flight,” Sotavalta wrote in a 1952 paper in Nature. In other words, because he had absolute pitch, Sotavalta was able to make wingbeat observations not only with cameras in the laboratory, but also in nature, with his ears. Scientists are informed and constrained by the senses they choose to use.
Nature was rather more consequential. There, Sotavalta describes the uses of his “acoustic method” of identifying insects using his absolute pitch, and theorises about the subtleties of insect wingbeat: how much energy it consumes, and how it varies according to air pressure and body size. Even so, only decades later did scientists such as Brydegaard reaffirm the relevance of wingbeat in the study of insects – for example, malaria-carrying mosquitoes.
Read the full fascinating article here at BBC