Biocontrol may be making invasives stronger

Natural enemies used to control invasive weeds could be helping them band together, not break apart, allowing them to thrive rather than decline, new research from Australia's University of New South Wales (UNSW) warned on Thursday.

The study reveals that biological control methods, such as introducing insects that feed on invasive plants, could be encouraging weeds to cooperate, making them even more resilient and harder to eradicate.

While biocontrols have long been used to suppress weed populations, their effectiveness may be overstated, according to the study published in Trends in Ecology & Evolution.

"I don't think we've been measuring the success of biocontrol agents correctly," said lead researcher Stephen Bonser from the UNSW School of Biological, Earth & Environmental Sciences.

Success has been measured by how well biocontrol agents damage individual plants, but the bigger picture, how plant populations behave as a whole, is being overlooked, Bonser said.

The research suggests that by damaging the competitive traits of individual weeds, herbivores may inadvertently encourage group cooperation among the plants. Instead of racing to outgrow each other, the weakened weeds shift energy away from competition and into collective growth, allowing them to dominate landscapes more effectively.

"What we think is happening is that the biocontrol agents are turning aggressive invaders into cooperative communities, and when they cooperate, they can cover massive areas, even more than before," said Bonser whose team is now investigating new strategies to counteract this unintended effect, such as reintroducing tall native plants to break up weed cohesion, or combining biocontrol with other interventions.

(Cover: Egg masses of golden apple snails on rice stalks in Baoshan City, Yunnan Province, southwest China, September 7, 2024. /VCG)