Chemicals are changing insects in subtle yet deadly ways

While insects like stink bugs and mosquitoes might not be liked by many people, they play an essential role in maintaining the balance of Earth’s ecosystems.

E.O. Wilson, a renowned biologist, once emphasized their importance by stating that if insects were to vanish, the environment would collapse. 

However, scientists have recently observed a decline in insect populations, with numbers dropping by 2-3% annually, alongside shifts in their behavior.

This decline has driven researchers to explore potential causes, including habitat loss, climate change, and the effects of chemicals.

Effects of agrochemicals on insects

A study led by researchers from the European Molecular Biology Laboratory (EMBL) sought to understand how pesticides, herbicides, and other agrochemicals influence insect populations. 

Using more than 1,000 chemical compounds from EMBL’s unique chemical library, they systematically exposed fruit fly larvae to assess changes in their development, behavior, and survival throughout their life cycle.

The research revealed that 57% of the tested chemicals significantly altered fruit fly larvae behavior, even when the doses were not lethal. At higher exposure levels, the long-term survival of the flies was further compromised. 

“We found that when we exposed larvae to very low doses of chemicals, the exposure caused widespread changes in physiological processes that are at the heart of how they develop and behave,” said lead author Lautaro Gandara, a postdoctoral fellow at EMBL. 

Rising temperatures, chemicals, and insects 

The researchers also examined the effects of rising temperatures on these changes, simulating global warming trends.

To assess the influence of temperature, the team gradually increased the growing environment’s temperature, starting at 25°C (77°F) and raising it to 29°C (84.2°F). At this higher temperature, they observed a more pronounced impact on the larvae. 

“Further, we mixed some of the most commonly detected airborne chemicals, at ecologically relevant doses, again exposing fruit flies from when they first hatched. We then saw a much stronger effect,” said senior author Justin Crocker, a biologist at EMBL. 

Neurological and physiological disruptions 

These effects included a 60% reduction in egg-laying rates and the emergence of altered behaviors like “hunching.”

Hunching, where larvae curl their bodies excessively, can indicate stress or toxicity and may point to underlying neurological or physiological disruptions. 

“On the surface, hunching may seem inconsequential, but even small changes in behavior can impact fitness if they adversely affect feeding, mating, and migration,” Crocker explained. 

While the connection between hunching and reduced egg-laying remains unclear, it is likely that larvae preoccupied with such behaviors would struggle to thrive in the wild.

Chemical impact on insect behavior 

The study involved collaboration with several scientists, including Jean-Baptiste Masson and François Laurent from the Pasteur Institute, who provided AI-based tools to analyze behavioral changes. 

Additional partners included Heidelberg University Hospital and George Washington University, where the experiments were expanded to mosquitoes and Painted Lady butterflies. 

These efforts helped confirm that similar patterns emerged across different insect species, reinforcing the study’s conclusions.

“Insects – even those that can seem like pests – are critical to the planet. They pollinate the plants we eat and they’re an important part of the food web,” Gandara noted. 

The research sheds light on how even low doses of chemicals can have significant impacts on insect behavior and survival. This deeper understanding provides a clearer picture of the challenges insects face and the factors contributing to their decline.

Broader implications of the research

The study’s findings have significant implications for understanding ecosystem health and balance. 

As insect populations dwindle, genetic diversity decreases, making it harder for species to adapt to environmental changes. This threatens not only food webs but also the resilience of ecosystems against future challenges.

“The positive aspect to this work is that we have new knowledge about which chemicals can cause certain molecular changes and associated behavioral and developmental changes,” Crocker said. 

This knowledge could inform regulatory practices and industrial approaches that better protect both human health and the environment. 

By understanding the subtle but crucial ways chemicals affect insects, scientists can help create a more balanced approach to pesticide use, aiming for practices that support the health of these vital creatures.

The study is published in the journal Science.

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