Evaluations of insecticides to reduce transmission of Xylella fastidiosa in olives

The efficacy of several natural and synthetic compounds to suppress populations of Philaenus spumarius, the predominant EU vector of Xylella fastidiosa, has been investigated in the past recent years. As for many other vector-borne diseases, control strategies aim also to reduce the feeding events and therefore the chances of transmission. In this context, we evaluated the use of different compounds in reducing the rate of bacterial transmission in olives either under filed conditions or confined conditions in cages. In fields located in the infected area of Apulia (southern Italy), we tested the use of kaolin.  Healthy plants were sprayed for three consecutive years on a calendar basis with kaolin and imidacloprid (control product). Results showed that neither kaolin or imidacloprid protected plants from infections, however for both treatments a delay in the progression of the infections (n. of infected plants) and symptom severity were recorded compared to the untreated control plants. When kaolin was applied in cages, results were similar in that number of infected plants was lower for the treated plants than for the untreated plants. In cage trials, compounds tested included imidacloprid, acetamiprid, delthametrin, and phosmet. Experiments conducted in cages were set up using Xylella-infected spittlebugs (apprx. 15% of qPCR-positive specimens).  Insects were released in the cages after 3, 7 and 15 days after treatment (DAT) and maintained for 3 days for the inoculation access period. High mortality rates were recorded with all insecticides except for phosmet that showed inconsistent results. At 3 DAT, no infections were recorded on the seedlings sprayed with neonicotinoids and delthamethrin. Low or no infections were recorded with neonicotinoids and delthamethrin at 7 and 15 DAT, while rates of infections were similar for phosmet-sprayed and untreated controls.