Searching for native egg-parasitoids of the invasive alien species Halyomorpha halys Stål (Heteroptera, Pentatomidae) in southern Europe

Halyomorpha halys is an invasive species, originating from East Asia, which was accidentally introduced in some areas of North America and Europe, where severe damages to different vegetable crops and fruit plants were recorded. Several studies in different countries focused on the possibility to apply biological control by means of egg-parasitoids. The main egg-parasitoids in the original area are unfortunately non-specific and thus the application of classical biological control is questionable. On the other hand, the possibility of using augmentative biological control by native egg-parasitoids able to exploit the new host is an interesting possibility in both Europe and the USA. In a preliminary assay, frozen egg masses of H. halys were exposed in the field in central Italy. Results showed that some eggs were exploited by parasitoids belonging to the species Anastatus bifasciatus and Ooencyrtus telenomicida. Therefore, different native egg-parasitoids species widespread in Europe were tested in the laboratory in order to explore their ability to parasitize H. halys eggs. To this end, no-choice tests were carried out in climatic chambers (26°C, 70%RH, 16:8 L:D) in order to evaluate the parasitization potential of females collected in the wild. Conducted tests pointed out that A. bifasciatus and especially O. telenomicida may be potential candidates for the biological control of H. halys. In particular, O. telenomicida was able to parasitize the 35.56% of the exposed host eggs in the lab tests. New adults successfully emerged from the 22.92% of the eggs, and overall, this egg-parasitoid caused a significant hatching reduction of the H. halys eggs (more than 70%). Conversely, Telenomus chloropus and Ooencyrtus pityocampae were less promising species as biocontrol agents of this agricultural pest. Preliminary trials in pear orchards consisting of field releases of laboratory-reared specimens of O. telenomicida, one of the potential candidates for biological control, showed that this parasitoid is actually able to discover egg masses of H. halys (sentinel frozen egg masses) and to successfully parasitize them.