December 2024
Biocontrol uses substances, technologies or mechanisms derived from nature to control insect pests, diseases and weeds in agriculture and forestry. Biocontrol products generally fall into the following categories, depending on the “active ingredient” of each:
This article is one in a series providing case studies of biocontrol products that are on the market or under development in Europe.
Acacia longifolia, a small tree or shrub native to southeastern Australia, is an invasive species in Portugal and other parts of the world. In Portugal, it invades large areas of coastal ecosystems, replacing native plant communities with dense, woody stands. Its presence also alters soil chemistry and ecosystem functioning. Additionally, this invasive plant reduces forest productivity, particularly in coastal pine plantations, leading to negative economic impacts. The invasiveness of A. longifolia is in part due its ability to produce large quantities of seeds.
In 2015, Trichilogaster acaciaelongifoliae, an Australian bud-galling wasp, was approved in Portugal to fight against this invasive plant. This wasp lays its eggs on flower buds (and later on vegetative buds), causing the formation of galls instead of flowers, which reduces seed production and slows the spread of A. longifolia. The wasp has one generation per year, with most of its lifecycle spent as eggs, larvae and pupae within the developing galls.
The approval for this product in Portugal took 12 years, including tests on 40 plant species and extensive risk assessments by both national and European authorities. Galls for the initial tests and releases were sourced from South Africa, where the bud-galling wasp has been successfully used for more 30 years. Only female wasps were released due to their ability to reproduce asexually.
Despite initial challenges due to differences in seasonal cycles between hemispheres, the wasp showed effectiveness against the invasive plant. Its lifecycle only took 8–9 months to complete, shorter than an expected year. This suggests that future generations may fully adapt to northern hemisphere seasons and the lifecycle of A. longifolia. In 2017, second-generation galls were observed at some of the release sites and a significant increase in mature galls was recorded, indicating successful establishment of the wasps. This shows the potential for biocontrol to manage invasive plants and restore ecosystems.