Acoustic behaviour and flight tone frequency changes in adult Aedes albopictus and Culex quinquefasciatus mosquitoes

Species-specific wingbeat frequency of mosquitoes has already been shown to be useful in species identification. However, mosquito identification using their fundamental wingbeat frequency requires proper evaluation along with its morphological and ecological characters. An acoustic study was carried out on four species of laboratory reared mosquitoes Aedes albopictus, Culex quinquefasciatus, Anopheles crawfordi, and Armigeres subalbatus. However, a detailed study on wingbeat frequency and its variation at different points of the adult life stages was conducted for Ae. albopictus and Cx. quinquefasciatus. Recorded wingbeat beat frequency during the different point of adult life stages was analyzed using the Raven Pro 1.6.1 sound analysis software. Result showed that there was a significant difference in the fundamental frequency between four study species (F = 81.62; df = 151; p < 0.001). Wingbeat frequency of Ae. albopictus and Cx. quinquefasciatus observed to be low immediately after emergence from the pupal stage and gradually became peak during the swarming stage which is considered as the species' fundamental frequency. These change in wingbeat frequency during the early adult stages leads to uncertainty in species identification based on the fundamental frequency. Swarming and pairing activities in Cx. quinquefasciatus and Ae. albopictus exclusively depends on the convergence between male first harmonics (M₁) and female second harmonics (F₂) of their fundamental frequency and make combined harmonic frequency at 1400-1500 Hz. Interestingly, this study observed that the frequency of adult male and early stages of female did not converge at the M₁-F₂ harmonics, thereby preventing successful mating. It thus infers that the wingbeat frequency of active male and female have significant role in the selection of potential mates within the species.