Volatile Emission of Pear Tree (Pyrus communis) and Olfactory Perception of Pear Psyllids (Cacopsylla pyri and C. pyrisuga) are Affected by Elevated Tropospheric Ozone Concentration

Climate change and rising tropospheric ozone concentration are impacting ecosystems in various ways and can influence the volatile-mediated interactions between insects and their host plants. In this study, individuals of the psyllid species Cacopsylla pyri and C. pyrisuga as well as their host plant Pyrus communis were exposed to elevated but naturally occurring ozone concentrations. The effects on the olfactory perception of the insects and the volatile emission of the plants were examined. Ozone exposure affected the olfactory perception of C. pyri and C. pyrisuga. While the perception threshold of hexanal increased in C. pyri, the perception of the tested compounds was not impaired in C. pyrisuga. Behavioural tests with ozone exposed C. pyri revealed an unchanged repellent effect of nonanal, while hexanal and a synthetic volatile blend became repellent to this species. These findings show only minimal direct effects of moderate ozone concentrations on olfactory perception of pear psyllids. In contrast, chemical analysis of the host plant odours showed a dramatic change in the volatile composition during ozone exposure, with a statistically significant decrease of terpenes and an increase of aldehydes and ketones, showing a greater impact of ozone on the emitter than on the receiver in the pear-psyllid system. This study highlights that moderate ozone levels can alter volatile emissions, potentially disrupting host plant location and impacting other insect-plant interactions that depend specifically on volatile-mediated communication.