Starting an invasion: A five-year monitoring program of Halyomorpha halys (Hemiptera: Pentatomidae) in South Tyrol (Northern Italy)

Abstract

Monitoring action are a fundamental step when non-native species are invding new areas. The phytophagous pest Halyomorpha halys (Stål), originated from north-eastern Asia, is by now introduced in several countries worldwide. Its highly polyphagous behaviour, paired with a relatively high reproduction rate under favourable conditions, makes it an im-portant pest of several agricultural crops. In South Tyrol (Northern Italy), one of the largest con-tiguous apple growing regions in Europe, first adults had been reported in March 2016. Active monitoring techniques, as well as the implementation of a Citizen Science approach, enabled to follow up the spread and settlement of stable populations of H. halys in South Tyrol. Since its first detection, H. halys showed a rapid expansion of colonized area and an increase in population densities from year to year. Established populations coincide mostly with the main apple growing area, namely the Etsch Valley from Meran to Salurn, mainly occupying lower altitudes between 200 and 500 m a.s.l. Since 2019, a further spreading in the western and eastern parts of South Tyrol can be observed. In apple orchards H. hals showed generally a continuous presence throughout the growing season from April to October, with population peaks in the late season. On the other side, populations dynamics and densities of adults and nymphs differ significantly between years ans sureveyed sites. The findings indicate that the application of pheromone baited traps is a good tool for an area wide approach in or-der to get information on its spreading, to pinpoint the main distribution area and to draw a general picture of the population dynamics at a larger scale. On the other side, an area wide approach should be interpreted cautiously, as real population densities might be underesti-mated and do not depict the real situation for singular orchards.