Aclees taiwanensis: biology and spread of the invasive species recently introduced in Europe Aclees taiwanensis: biologia e diffusione della specie invasiva di recente introduzione in Europa

Aclees taiwanensis, the fig weevil, is a species native to Taiwan, accidentally introduced in Europe through the bonsai trees’ trading. It has been first detected in 2005 in Tuscany, in the nursery district of the Pistoia province. The pest is oligophagous on plants belonging to the genus Ficus, so it represents a threat primarily for the common fig Ficus carica. Adults feed on leaves and ripening infructescences, making them unsellable. The major damage is though caused by the xylophagous larvae which, digging alimentation galleries inside the trunk and surface roots, compromise the sap flow of the tree. The difficulty in promptly detecting and reaching the preimaginal stages inside the plants is one of the main limits to the control of the fig weevil. The biological and synthetic products tested so far have not been decisive and, despite its harmfulness, there are currently no regulations to limit its spreading. Therefore, specific strategies to detect and control A. taiwanensis, developed based on its biology and physiology, are needed. This research aimed to determine, under laboratory and field conditions, the main biological traits of the species. In the laboratory, the duration of the embryonic, larval, and pupal stages was verified. The pre-imaginal instars and adults’ morphometric measures were taken, and a reliable characteristic to discern the sexes was identified. We collected data about female fertility and fecundity and on the modalities of oviposition. Moreover, the susceptibility of Ficus benjamina, F. microcarpa, and F. pandurata, three ornamental species of economic value, was evaluated. In the field, through surveys carried out during 2019, the population dynamic was determined. In the end, by a citizen science approach, the current presence of the fig weevil in Southern Europe and its spreading from 2008 to 2020 were verified. Based on our results, the embryonic stage lasts about 10 days, the larval development almost 80, and the pupal about 23. Regarding the adults, females usually have longer rostra and bigger bodies than males, but the sexes can be discerned based on the different shape and position of the last abdominal tergite. Each female lays more than 100 eggs (in the soil or cracks of the bark), of which, in the laboratory, almost 70% hatch. The three ornamental Ficus species tested have been defoliated, although in different manners and timing. Among these, A. taiwanensis was able to reproduce only on F. macrocarpa. In the field, adults have been captured all-year-round with three population peaks. The current distribution of the pest in seven northern and central Italian regions and the Provence-Alpes-Côte d’Azur region in southern France (identified through the citizen science approach) suggests that, without effective control strategies, the further spread of A. taiwanensis is predictable. This especially in the Southern Italian regions and the Mediterranean basin where fig cultivation is one of the most ancient and characteristic.