Mapping the auditory space of Culex pipiens female mosquito in 3D

Abstract

The task of directional hearing faces most of the animals that possess ears. They approach this task in different ways, but the common trait is the usage of the binaural cues to find the direction to the source of sound. In insects, the task is further complicated by their small size and, hence, minute temporal and level differences between two ears. A way to overcome this problem is to receive the particle velocity component of sound rather than the pressure, as the former naturally involves directionality. However, even in this case, one ear is not enough for directional hearing: a single symmetric flagellar particle velocity receiver cannot discriminate between the two opposite directions along the vector of the sound wave. Insects that use flagellar auditory organs, and mosquitoes in particular, possess a pair of receivers, which presumes the usage of binaural hearing. Its mechanisms are expected to be significantly different from the ones typical for the pressure receivers. However, the directionality of flagellar auditory organs has received little attention. Here we measured the in-flight orientation of a female mosquito antennae and obtained detailed physiological mapping of the Johnstons organ directionality at the level of individual sensory units. By combining these data, we provided a three-dimensional model of the mosquitos auditory space. The natural orientation of the antennae together with angular distribution of sensory units in each of the Johnstons organs was found to be optimal for binaural hearing focused primarily in front of, above and below a flying mosquito.