Influence of the temperature on the acquisition efficiency of Xylella fastidiosa by Philaenus spumarius

Given the wide range of latitudes at which the bacterium Xylella fastidiosa (Xf), susceptible host plants and insect vectors may coexist, we have investigated the effect of different range of temperatures on the capability of Philaenus spumarius, the predominant insect vector of Xf  in Europe, to acquire and transmit Xf from olive to olive. Plants cv Cellina di Nardò infected with Xf susbsp. pauca ST53 were exposed at the following conditions: 38-32°C; 36-28°C; 32-24°C; 28-20°C; 20-14°C. More specifically, to simulate day/night conditions, in each treatment, plants were daily exposed for 10h at the highest temperature, then for 14h at the lowest one. Infected source plants were pre-conditioned at the same temperatures either for 3 or 8 days before starting the experiments. 
After an acquisition access period (AAP) of 3 days, insects were moved to receptor plants maintained at the same temperatures of the correspondent AAP. Insect mortality was recorded after both AAP and IAP, whereas the acquisition of Xf was estimated by qPCR on individual insects tested after the IAP. As the experiment is still ongoing, herein we report only the data on the AAP. Briefly, mortality reached average values of 99-100% when insects were caged on the plants maintained at 38°C; it dropped to approx. 60% at 36°C, and to 20-30% at 28°C and 32°C, respectively, while at 20°C it was less than 10%. 
The acquisition rate could not be estimated for the highest temperature (due to the high mortality). Acquisition was lower at 36°C (about 9%), compared to the other tested temperatures (about 35%). Only at the highest temperatures, pre-conditioning the plants for 8 days reduced the AAP efficiency compared to 3 days pre-conditioning, suggesting an effect of the high temperature on the bacterium in the host plant. Although limited to the AAP, these results demonstrate a significant impact of high temperatures (> 32°C) on insect survival and Xf acquisition efficiency.