Figure 4.

Examples of harmonic convergence, viewed in the form of a frequency time plot. Convergence is typified by one or both of the mosquitoes altering their wing beat frequency so that harmonic components approximately converge to some low integer ratio, for a period lasting up to tens of seconds. The relevant frequency components are shown with zoomed-in frequency axis (over the same time) below. The data presented here are extracted using Hilbert spectral analysis, and show convergence at female : male integer ratios of (a) 3 : 2 and (b) 2 : 1. At this resolution the imperfect nature of frequency convergence between the insects is apparent.