Dispersal ability ofNeophilaenus campestris, a vector ofXylella fastidiosa, from olive groves to over-summering hosts

Abstract

SUMMARYNeophilaenus campestris is one of the recently identified spittlebugs (Hemiptera: Cercopoidea) able to transmit Xylella fastidiosa to olive trees. Considering its vector ability and the wide distribution of this species in Spain, N. campestris should be considered a serious threat to key crops that are vital for Spanish agriculture such as olive, almonds and grapevines. Migration and dispersal abilities of insect vectors have profound implications in the spread of vector-borne diseases. Thus, knowledge on the dispersal ability of N. campestris is essential to model, predict and limit the spread of the diseases caused by X. fastidiosa. A mark-release-recapture technique was developed to track between-field movements of N. campestris during its late spring migration from the ground cover grasses within olive groves to sheltered areas dominated by pine trees. An indoor assay showed that the fluorescent dust used for marking did not affect the survival nor the flying ability of N. campestris. Spittlebug adults captured in olive groves at Los Santos de la Humosa (Madrid, Spain) during late spring, 2019 were dusted with four fluorescent colours and released in four different locations. Six recapture samplings were performed 23 to 42 days after release in 12 different sites located within a maximum distance of 2.8 km from the release point. Results indicated that N. campestris was able to disperse a maximum distance of 2473 m in 35 days from the olive groves to areas dominated by pine trees. Furthermore, our flight mill studies also showed that N. campestris was able to fly long distances, reaching almost 1.4 km in an 82 minutes’ single flight.Moreover, we carried out a survey of directional movement of potential vectors of X. fastidiosa in an olive grove located in Villa del Prado (Madrid). We used yellow sticky bands, a Malaise trap and a vertical yellow sticky net to assess the directional movement from olive groves to surrounding managed and unmanaged areas. The captures obtained in the yellow sticky bands showed that spittlebugs dispersal from the olive grove to surrounding vegetation matched with the time when the ground cover dried out. The highest number of spittlebugs was captured in the border between the olive grove and a vineyard close by.Altogether, our findings suggest that eradication measures by rooting-up X. fastidiosa-infected and non-infected trees in a radius of 100 m are of limited value because vectors are able to disperse rapidly over distances much longer than expected.

Dispersal ofPhilaenus spumarius(Hemiptera: Aphrophoridae), a Vector ofXylella fastidiosa, in Olive Grove and Meadow Agroecosystems

“…A recent study carried out in Spain on the dispersal of N. campestris —another European spittlebug species—has highlighted the flying capabilities of this species, which is able to disperse for long distances in a mixed agricultural landscape (300 m in 8 d and up to 2 km in 35 d) ( Lago et al 2020 ). The high dispersal capabilities observed for N. campestris by Lago et al (2020) is only apparently in contrast with our estimates for P. spumarius, as several factors could have affected their results: 1) the influence of the smaller size of N. campestris , compared to P. spumarius , on both the active fly capabilities and wind dispersal ( Angelibert and Giani 2003 , Jenkins et al 2007 ); 2) the migration behavior, which is different from the dispersal behavior and is characterized by an escape movement to abandon a habitat ( Schneider 1962 ). Since their study was conducted in a summer period, when the ground vegetation has dried out under the Mediterranean climate, the insects were forced to move to patches with woody plants in order to have succulent foliage for aestivation ( Drosopoulos et al 2010 ); 3) the host-plant association of N. campestris adults, which mainly feed on coniferous plants (especially Pinus spp.)…”

“…( Bodino et al 2020 ). Furthermore, Lago et al (2020) did not consider the distribution of the proportion of the marked population over different distances from the release points, thus it is also possible that the individuals recaptured at 2 km from the release point were a very small portion of the population mainly dispersed at closer distances from the release point. In fact, 80% of the recaptured insects were found at 130–280 m from the release point, thus on average having moved 3.6–6.5 m/d.…”

“…However, given the low recapture rate, we did not observe any differences in the dispersal of P. spumarius adults for different periods of the year or between sexes. Moreover, the spittlebug movement dynamics at a landscape level is still largely unknown, though it is known to influence the abundance of insects and the presence of bacterium reservoirs outside crops ( Cruaud et al 2018 , Santoiemma et al 2019 , Lago et al 2020 ). Future studies should be aimed at improving the recapture rate of marked spittlebugs, possibly using both sweeps (efficient and precise but a time-consuming method) and sticky traps (less efficient and precise but which allow the number of both recapture points and recaptured insects to be augmented) ( Morente et al 2018 ).…”

“…Spittlebug adults are considered poor fliers, as they often just walk or jump instead of flying ( Weaver and King 1954 , Cornara et al 2018 ). Nonetheless, according to Weaver and King (1954) , these insects can move up to 300 m in 1 d, and a recent study, using a flight mill, has suggested that they can move up to 1,000 m in a single 1 h flight ( Lago et al 2020 ). Spittlebugs fly mainly at herbaceous vegetation level (15–70 cm), with only a small proportion found above this level, although a few individuals were collected up to a height of 84 m ( Freeman 1945 , Weaver and King 1954 , Halkka et al 1971 , Reynolds et al 2017 ).…”

“…The only MRR study concerning P. spumarius reported in literature managed to recapture only one specimen out of 418 marked at about 50–200 m of distance from the release point, and thus was not able to provide any useful information on the dispersal of this species ( Halkka et al 1967 ). In a recent MRR study carried out in Spain with another spittlebug species, i.e., Neophilaenus campestris (Fallén), a few individuals were found at up to 2 km from the release point ( Lago et al 2020 ).…”