Phytoplasma infection induces changes in vibrational signals of Cacopsylla pyri: sex-specific shifts in frequency, amplitude, and timing.

The pear psyllid (Cacopsylla pyri), the main vector of 'Candidatus Phytoplasma pyri', relies on substrate-borne vibrational signals for mate recognition and duet coordination. As pathogens can alter insect communication, we examined whether phytoplasma infection alters key parameters of male and female mating signals. We used laser vibrometry on a standardised artificial substrate, as well as playbacks, to examine this. We detected sex-specific differences in individual signal parameters. In males, infection significantly reduced the amplitude of chirps, whereas uninfected males showed a markedly higher number of interruptions within their trill units. Infected females produced longer inter-chirp intervals and showed higher dominant spectral components than uninfected females. However, fundamental frequency remained stable across treatments, suggesting that differences in dominant frequency reflect shifts in spectral energy among harmonics rather than changes in the primary oscillation frequency. These infection-induced changes may reflect physiological constraints affecting vibrational mechanics. These findings suggest that infection-related differences in dominant frequency reflect changes in the distribution of spectral energy among harmonics rather than a change in the fundamental frequency. Despite these differences at the individual level, the preliminary results of duet communication between males and females did not differ significantly across the various infection treatments. This suggests that the basic coordination in the duet may not be significantly impaired under laboratory conditions; this should be investigated more closely in a specially designed experiment.