Worldwide, habitat loss and biodiversity decline are accelerating, with a disproportionately large impact on existing ecosystems. Biological invasions by non-native plants are recognised as a major contributing factor. As part of his PhD research at Vrije Universiteit Brussel (VUB), biologist Gianmarco Minuti examined how the Yellow Iris (Iris pseudacorus), a plant widely known as the emblem of Brussels, has over the past few centuries spread far beyond its native range, becoming invasive across much of the world. Minuti’s work explores how its unchecked growth in regions like North and South America, and Southern Africa, can be managed using biological control methods.
“Classical biological control—the use of natural enemies to regulate invasive species populations—offers a sustainable solution for managing non-native plants,” explains Minuti from the VUB Research Group on Ecology, Evolution & Genetics. “In my thesis, I followed the key stages of a biological control programme targeting the Yellow Iris. This marks, to our knowledge, the first time a Belgian institution has participated in such an effort abroad.”
The Yellow Iris, native to Europe, North Africa, and Western Asia, has been classified as invasive in parts of North America, South America, South Africa, and Asia. Its global spread was largely driven by ornamental trade exports, from which it frequently escaped cultivation and colonised temperate wetlands worldwide.
Minuti’s research began seven years ago during his MSc studies, focusing on biological control as a potential management strategy. Field surveys in the plant's native range identified three natural enemies as candidate biological control agents, with particular attention to the Aphthona nonstriata flea beetle.
These tiny beetles, just a few millimetres long, feed on Yellow Iris leaves, their host plant. Overwintering in leaf litter, they emerge in spring to devour the plant's foliage. Females lay eggs on the leaves, and by late May, the hatched larvae burrow into the roots and leaves, significantly weakening the plant by targeting its underground nutrient stores.
“We used climate-niche models to predict the current and future suitability of the plant’s range and its potential biological control agents,” says Minuti. “This helped us identify regions at the highest risk of invasion and assess how climate change could affect the effectiveness of biological control in those areas.”
Laboratory experiments demonstrated the flea beetle’s effectiveness in curbing Yellow Iris growth. “We observed significant impacts on the plant’s growth and photosynthesis, particularly in early developmental stages, suggesting the potential to control seedling populations.”
Minuti highlights the promise of biological control not only for the Yellow Iris but for managing a wide range of invasive weeds. However, he laments that such methods are rarely implemented in Europe. “Despite being used effectively in other parts of the world for over a century, biological control remains underutilised here,” he notes.
This research underscores the importance of sustainable solutions to manage invasive plants and protect ecosystems from further degradation.