Researchers Warn of Fungicide's Impact on Insect Populations
- The Earth & I Editorial Team
- Aug 22
- 3 min read
Chlorothalonil Seen as Detrimental to Fertility of Fruit Flies, Pollinators
A recent study led by researchers at Macquarie University in Australia has raised concerns about the widespread use of chlorothalonil, a commonly applied fungicide, and its potential to harm insect populations.
The study, published in Royal Society Open Science, reveals that chlorothalonil, even in concentrations typically found on food crops like cranberries and wine grapes, can substantially impair the reproduction of insects, posing serious risks to biodiversity and ecosystem stability.
The pesticide is banned in the European Union. Although allowed in the US, the US Environmental Protection Agency (EPA) has classified chlorothalonil as a likely human carcinogen.
Researchers are increasingly concerned about the decline in insect populations worldwide—a phenomenon referred to as the “insect apocalypse.” Insect populations have been plummeting by more than 75% in certain regions over the past few decades, with potentially devastating effects on ecosystems.
Targeting the Fruit Fly
The research, conducted by PhD candidate Darshika Dissawa from Macquarie's School of Natural Sciences, focused on the impact of chlorothalonil on Drosophila melanogaster—better known as the fruit fly.
According to the study authors, although fruit flies are not a target of agricultural fungicides, they serve as a model organism for studying the broader ecological effects of such chemicals due to their “genetic tractability, short life cycle, and well-documented sensitivity to a broad range of environmental contaminants.” The study showed that even the lowest levels of chlorothalonil had a detrimental impact on the fertility of these flies, affecting both males and females.
The capacity for detoxification of chlorothalonil could vary across insect species. For instance, due to genetic differences, honeybees could potentially be more susceptible to chlorothalonil than fruit flies.
"Even the very lowest concentration has a huge impact on the reproduction of the flies that we tested."
“Even the very lowest concentration has a huge impact on the reproduction of the flies that we tested," Dissawa told Macquarie’s news outlet, The Lighthouse, in June. “This can have a big knock-on population impact over time because it affects both male and female fertility.”
Fruit flies are “also at the bottom of the food chain, becoming food for a whole lot of other species,” added Dissawa.
Striking Results
The study exposed D. melanogaster larvae to chlorothalonil concentrations corresponding to those typically found in agricultural environments. The results were striking: the flies exhibited a 37% reduction in egg production at maturity compared to control flies that were not exposed to the chemical.
“We expected the effect to increase far more gradually with higher amounts. But we found that even a very small amount can have a strong negative effect,” explained study supervising author, associate professor Fleur Ponton.
Chlorothalonil Widely Used
Chlorothalonil is frequently used in Australian agriculture, particularly in orchards and vineyards, to control diseases like mildews and leaf blights. However, this fungicide has been detected in nearby soils and water bodies, with residue levels in fruits and vegetables ranging from trace amounts to as high as 460 milligrams per kilogram. Despite being banned in the EU over environmental risks, chlorothalonil continues to be widely used in other parts of the world.
“People assume fungicides only affect fungal diseases, but they can have unintended, devastating consequences for other species.”
“People assume fungicides only affect fungal diseases, but they can have unintended, devastating consequences for other species,” said Ponton. “We need bees, flies, and other insects for pollination, and this is an important issue for pollinator populations,” she added.
Reassessment of Agricultural Practices Needed
This research highlights a significant gap in the regulation and understanding of pesticide impacts. Despite being one of the most widely used fungicides in the world, fewer than 25 scientific studies have examined chlorothalonil’s effects on insects. “There is a strong need for more research to understand the long-term consequences of these chemicals, especially as insect populations continue to decline,” Ponton told The Lighthouse.
The study calls for a review of agricultural practices, including a reduction in pesticide use to allow insect populations to recover. “We need field trials to explore alternatives and develop evidence-based guidelines to mitigate the effects of fungicides on beneficial insects,” Ponton concluded.