Abstract
The yellow‐legged Asian hornet is an invasive species of wasps, indigenous of the South‐East Asia but quickly spreading in Southern Europe. Because of its exponential diffusion and its serious threat to the local honey bee colonies and to humans as well, restraint measures are under investigation. Among them, the harmonic radar described in (Ecology and Evolution, 6, 2016 and 2170) already proved to be a quite effective way to follow the hornets to their nests; it is in fact capable of tracking the flying trajectory of these insects, once equipped with a small transponder, in their natural environment. The aforementioned harmonic radar was upgraded after a period of intense experimentation; the capture of the hornets was enhanced as well, and other improvements were adopted in the mounting procedure of the transponder. Thanks to these upgrades, the flying capabilities of the hornets were not reduced and a huge collection of data was recorded. The main upgrade to the radar was the adoption of the vertical polarization of the radiated field, with the consequent redesign and manufacturing of the antennas and the different mounting of the transceiver on the insect. The installation of the radar on a telescopic tower drastically improved the maneuverability of the system and the capability to follow the insects’ preferential flying directions. Eventually, the system was able to produce much more continuous traces with a clear indication of the most probable position of the nest. The maximum range of detection was also increased to 150 m.
Highlights
Vespa velutina arrived in Europe in 2004 (Haxaire, Bouguet, & Tamisier, 2006) and quickly spread despite numerous attempts to control it (Demichelis, Manino, Minuto, Mariotti, & Porporato, 2014; Rome et al, 2013); different types of traps and baits were used to restrain it, together with the destruction of the found colonies
As stated while describing both the transponder and the antenna properties, a vertical tag hit by a vertically polarized field always retransmit a signal back to radar, producing a far more continuous trace with respect to the previous setup; as long as the tag stays in the detection range of the radar and it is not shielded, a returned signal is observed
The introduction of the telescopic tower helped to have detections beyond closest obstacles, for instance an olive wood located southeast with respect to the radar position “A”; rather, continuous detections were seen about 50 m inside the olive wood, indicating that the flight trajectories can be followed in very challenging conditions too
Summary
Vespa velutina arrived in Europe in 2004 (Haxaire, Bouguet, & Tamisier, 2006) and quickly spread despite numerous attempts to control it (Demichelis, Manino, Minuto, Mariotti, & Porporato, 2014; Rome et al, 2013); different types of traps and baits were used to restrain it, together with the destruction of the found colonies (see Monceau, Bonnard, & Thiéry, 2014). As documented in Bertolino, Lioy, Laurino, Manino, and Porporato (2016), the area occupied by the these hornets in Italy increased from 205 km in 2013 to 930 km in 2015; the front line was at 55 km along the coast from the French border in 2015, with a linear spread of 18.3 ± 3.3 km/year. A cluster analysis of the range allowed the identification of 17 core areas used by the hornets, with a mean nest density of about 2.9–3.5 nests/km. A cluster analysis of the range allowed the identification of 17 core areas used by the hornets, with a mean nest density of about 2.9–3.5 nests/km2 These numbers are of paramount importance to monitor the evolution of the diffusion
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