Establishment, spread and early impacts of the first biocontrol agent against an invasive plant in continental Europe - Source dataset

This dataset was the base of the study entitled "Establishment, spread and early impacts of the gall-forming biocontrol agent Trichilogaster acaciaelongifoliae in Portugal" by López-Núñez et al. (2021)

Classical biocontrol is seen as being pivotal for the successful management of invasive alien plants, but is a relatively new concept in Europe. Although post-release monitoring in biocontrol programs is critical to evaluate the efficacy of a biological control agent, this is often neglected. The Australian bud-galling wasp Trichilogaster acaciaelongifoliae (Frogatt) (Hymenoptera: Pteromalidae) is used to control the invasive Acacia longifolia (Andr.) Willd., with a long history of success in South Africa. This biocontrol agent was first released in Europe in 2015 at several sites along the Portuguese coast.
We monitored the establishment, spread and early impacts of T. acaciaelongifoliae on target-plants in Portugal, across 61 sites, from 2015 to 2020. Initial releases of adults emerging from galls imported from South Africa and the subsequent releases from galls established in Portugal was compared, assessing the implications of a hemisphere shift. The impacts on the reproductive output and vegetative growth of A. longifolia were evaluated in more detail at three study sites.
From 2015 to 2019, 3,567 T. acaciaelongifoliae were released at 61 sites, with establishment confirmed at 36 sites by 2020. The transfer of the wasp from the southern hemisphere limited its initial establishment, but increased rates of establishment followed with synchronization of its life cycle with northern hemisphere conditions and releases of adults from galls that established in Portugal. After an initial modest establishment, T. acaciaelongifoliae adapted to the northern hemisphere conditions and there was an exponential increase in presence of galls (> 24,793 galls by 2018). Galled A. longifolia branches produced significantly fewer pods (84.1%), seeds (95.2%) and secondary branches (33.3%) and had fewer phyllodes but better growth of the main branch compared to un-galled branches.
'Synthesis and applications' – This study reports the detailed post-release monitoring of the first biocontrol agent intentionally introduced against an invasive plant in continental Europe. Trichilogaster acaciaelongifoliae successfully established in the northern hemisphere, despite the phenological mismatch and adverse weather conditions. To achieve this, it had to establish and synchronize its life cycle with that of its host-plant, after which it developed exponentially and began to show significant impacts on the reproductive output of the target plant.