An immunomarking method to investigate the flight distance of the Japanese beetle

Popillia japonica Newman (Coleoptera: Scarabaeidae), a devastating pest to many crops and other plants, has been detected in the European mainland for the first time in 2014 in Northern Italy. Official measures have been immediately implemented to contain the spread of this insect, and studies to evaluate its dispersion rate have been rapidly launched. The flight activity of beetles has been studied in 2017-19 using a protein immunomarking technique (PIT), by spraying either chicken egg white (marker: albumin) or cow milk (casein) on infested plants. Sampling of potentially marked beetles occurred up to a distance of 12 km with double lure baited traps, and markers were identified via two indirect ELISAs assays (anti-egg and anti-milk). Females were dissected to assess egg load and relate it to distance travelled. Data were handled with geostatistical methods (indicator kriging, IK). Collectively, about 1600 beetles were captured and analyzed. Rates of marked beetles ranged 7-15% for albumin and 2-22% for casein. Mean distances travelled ranged 1-7 km from sources; however, a few marked beetles have been found to disperse up to 12 km (maximum distance investigated). Geostatistical analyses showed that the spatial dependence of marked beetles occurred up to 2.3 km distance. Egg load in marked females was not related to distance travelled. The results of this research, examined together with field surveys carried out by the Plant Protection Service, could provide useful guidance in establishing an effective radius for the demarcated area.