Which treatment is most effective at reducing the damage caused by the pest box tree moth? A case in a Mediterranean...

Boxwood (Buxus sempervirens) is an important element of the European plant landscape. Currently, this species is seriously threatened due to the high impact of the pest box tree moth (Cydalima perspectalis). This lepidopteran is an invasive species of Asian origin that feeds exclusively on the genus Buxus. Management of this pest is necessary, but field trials are lacking. The aim of this study is to provide robust information about the effectiveness of the three major control methods currently available through a case study on a Mediterranean mountain. These treatments include the application of Bacillus thuringiensis and mass capture with sex pheromones in combination with the use of parasitoids of the genus Trichogramma. The experiment was carried out at Pla Boixer, NE Iberian Peninsula. Between 2020 and 2022, damage to boxwood was sampled and analysed at different scales. The results show that Bacillus thuringiensis reduced defoliation by 53%, whereas mass trapping only preserved regrowth with no significant reduction in damage (p > 0.05). Trichogramma releases did not significantly affect damage levels, nor in combination with other treatments. The treatment with B. thuringiensis protected the boxwood from defoliation but its use should be limited to specific cases in which boxwood is highly affected at the regional scale because of its impact on ecosystems and the difficulty of its application. No seasonality was observed in the damage; however, regrowth showed a favourable trend from spring to autumn. These insights should be considered in future management plans for this pest.