Evaluation of sticky traps for monitoring spittlebugs, the main vector species of X. fastidiosa in Europe

Upon the discovery of several European outbreaks of the quarantine bacterium Xylella fastidiosa, intense research programs and extensive surveys have been settled to tackle the insect vector populations responsible for the spread of the infections in the outbreaks. These investigations have clearly showed that the spittlebugs Philaenus spumarius L. and Neophilaenus campestris (Fallén) are the most common vector species, being frequently captured in crops and natural environment. Moreover, transmission experiments demonstrated their ability to acquire and transmit the most aggressive bacterial strain so far known in Europe, which is causing the severe epidemics on olives in the Apulia region (southern Italy). Given the detrimental impact of this epidemic spread, monitoring the presence of spittlebugs in different crops in this region, is relevant for the implementation of vector control strategies. To this end, between 2018 and 2019, sticky traps were evaluated as tool for monitoring the insect populations in olive, almond and cherry orchards from late spring to late summer when adults are known to occur. In 2018, different coloured sticky traps (white, red, blue, yellow, yellow with circle-pattern and yellow with line-pattern (Russel IPM, UK) were initially tested to determine the most attractive colour. Overall, the results showed that the yellow sticky traps were the most attractive for both spittlebugs when compared to white, red and blue traps. Thus, a large field validation was then carried out in 2018 and 2019, to further compare the efficiency of these three yellow-coloured traps, to assess the effects of trap height. Traps were inspected and changed every two weeks and concomitantly sweep netting was also carried out for a comparative assessment. The results indicated that an integrated use of both approaches can be very useful for monitoring the presence and the dynamics of the adult populations in crops and natural environment. More specifically, sweep net were more efficient in capturing insects soon after the emergence of the adults, whereas later on in the season the yellow sticky traps yielded higher performance in capturing the adults moving from one vegetation compartment to another (i.e. from the ground vegetation to tree canopies). Yellow sticky traps were more efficient than sweep net in orchards with medium population density, whereas no significant differences were recorded between the two applied methods in orchards with high population density. In situation with low population density, traps were less efficient although still provided evidence on the presence and occurrence of the target species. Overall, the combination of both approaches can effectively support monitoring programs for vectors controls, in particular to support surveys for spittlebugs in the so called "demarcated areas" where control actions are mandatory or highly recommended to control the vector populations.