What if an insect managed to wipe out an invasive tree?

The long-leaved wattle is one of the main threats to the ecosystems of the southwest Alentejo’s dunes, causing damage also to agricultural fields.


Control of this invasive species is very complicated, as it produces a bank of millions of seeds in the soil that remain viable for decades. When acacia trees are cut, thousands of seeds germinate, quickly regenerating the acacia forest.

In 2015, and after twelve years of studies, was introduced in Portugal a method of biological control for this acacia that prevents the production of seeds. The natural enemy is a small Australian insect called Trichi galls (Trichilogaster acaciaelongifoliae), from long-leaved wattle’s same region of origin, which lays its eggs in the buds that originate the acacia’s flowers. When the flower buds receive the insect’s eggs, the plant “reacts”, forming a gall (or bugle) instead of the flowers.

Without flowers, there are no pods (the fruits) and without pods, there are no seeds. In the short term, the areas affected by this insect no longer have new seeds in the soil, which reduces the species ability to spread to adjacent areas. In the medium term, it is expected that the areas where this invasive species is removed can be colonized by native species, as there will no longer be viable seeds in the soil.

In 2021, by BIGEO – Living Science Club of Odemira Secondary School -, several galls of the wasp Trichilogaster acaciaelongifoliae were introduced in several places of Odemira’s coast. The insect has made an effective attack, and some trees have not produced any seed pods this year. However, the wasp’s speed of dispersal is low, as it only spreads a few hundred meters per year. Therefore, it’s important to multiply biological combat sites, a task that will be carried out along 2023’s spring.