Ordinary farm fungicides destroy insect reproduction

Bactericides that are widely sprayed on fruits and vegetables to prevent crop diseases are quietly devastating insect populations and are crucial for pollination and ecosystem health.

Macquarie University research shows that one of the world’s most widely used agrochemicals, even at the lowest concentrations routinely detected on food, can harm insect reproduction and survival. These findings have increased concerns about global insect decline, with some regions already reporting a 75% decline in population in recent decades.

The study, published in the Royal Society’s Open Science, reveals the disturbing gap in pesticide regulation: Despite the ubiquitous weeds, fewer than 25 scientific papers have examined their effects on insects, leaving regulators largely blind to their ecological impact.

Surprisingly toxicity at trace levels

“Even the lowest concentration has had a huge impact on the replication of the flies we tested,” explained Darshika Dissawa, a PhD candidate at the Macquarie School of Natural Sciences. “Over time, this can affect both men and women’s fertility, which can have a big impact on knocking crowds.”

The researchers exposed fruit fruit flies to chlorothiomycin concentrations, matching the concentrations commonly found in agricultural products from cranberries to wine. Even in the lowest dose tested (5 mg per kg), egg yield decreased by 37% compared to unexposed individuals. Reproductive output dropped by 58% at the higher concentration matching levels found in certain fruits and vegetables.

The team also found that exposure to chlorothione significantly reduced the number of ovaries (the production structure of female insects), while the disruption of male iron metabolism, which is crucial for sperm development and fertility.

Not just reproductive damage

The influence of chemicals extends to the reproduction range of basic survival processes:

• The larval mortality rate increases dramatically with exposure, establishing a fatal concentration that affects 50% of the larvae, while only 13.7 mg per kilogram
• Surviving larvae take longer to develop, suggesting metabolic destruction
• A significant loss of weight in women indicates overall adaptive disorder
• Male iron levels drop by half, potentially damaging fertility by destroying sperm production

A wide range of environments exist

The widespread use of Chlorothalonil provides inevitable exposure to insects across agricultural landscapes. Bactericides are often used to prevent and, even in the absence of disease, often coincide with the most active flowering periods of pollinators. The polluted pollen and nectar were brought back to the beehive, exposing the entire colony.

Supervisor Associate Professor Fleur Ponton expressed surprise at the efficacy of the chemical: “We expect a gradual increase in effect with more quantities. But we found that even small quantities can have a strong negative impact.”

Chemicals are targeted by proteins and glutathione components of the sulfur-cell defense system. While effectively resisting fungi, this mechanism has proven to be destructive to beneficial insects, destroying their ability to neutralize oxidative stress and maintain cell health.

Regulatory blind spots

Although the EU is banned in the EU due to health and environmental concerns, it is still widely used on Australian crops, including orchards and vineyards. The study reveals a key knowledge gap: Despite being one of the most extensive fungicides in the world, its impact on non-target insects has received the least scientific attention.

This negligence is particularly worrying given that insects (such as fruit flies) play an important ecological role outside of pollination. They help nourish bicycles, serve as food for birds and other animals, and help maintain ecosystem stability. Population decline can be cascading through food webs, affecting the entire agricultural and natural systems.

Associate Professor Ponton stressed: “We need bees, flies and other beneficial insects to pollinate, which we think is an important issue for pollinator populations.”

The researchers recommend using more sustainable practices, including a reduced frequency of application, to give insect populations time to recover between treatments. They also advocate better integration of phytobactericides derived from plant compounds that provide effective disease control and are less toxic to beneficial species.

As insect populations worldwide face increasing pressures on habitat loss and climate change, the study highlights how neglected agrochemicals accelerate the decline of species necessary for food security and ecosystem health.

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