How Pesticides and Climate Change Shape Insect Behavior and Survival
As global insect numbers decline by an estimated 2-3% each year, scientists are urgently investigating the root causes of this downward trend. Several factors, including habitat loss, climate change, and increased chemical use, appear to be contributing to both behavior shifts and dwindling populations, prompting researchers to delve deeper into the problem.
A recent study by EMBL researchers, in collaboration with a broader scientific network, sought to understand how various agrochemicals impact insects. They exposed fruit fly larvae to more than 1,000 distinct compounds from EMBL's vast chemical library, which contains a range of pesticides and herbicides. This methodical approach allowed researchers to evaluate each chemical’s impact on larval development and behavior across various geographic fly populations.
The larvae were observed through their entire life cycle, monitoring changes in development speed, behavior, and survival. Surprisingly, 57% of the chemicals tested caused notable behavioral shifts in the larvae, even at non-lethal doses. Higher chemical exposure levels further reduced long-term survival. “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 Lautaro Gandara, the study’s lead author and EMBL postdoctoral fellow. “These changes were exacerbated when we increased the temperature in the growing chambers by four degrees -- a decision born from the idea that global temperatures have been on the rise and might affect how pesticides affect the larvae.”
Seeking to simulate rising global temperatures, scientists raised the incubation environment’s temperature incrementally, first by two degrees Celsius and later to 29°C (84.2°F). The resulting effects were stark, indicating that small temperature increases could dramatically amplify the impact of certain chemicals.
In a subsequent experiment, the team blended commonly found airborne chemicals at concentrations typical of ecological exposure and tracked newly hatched flies. The effects became even more severe, with egg-laying rates plummeting by 60% and larvae displaying unusual behaviors, such as increased “hunching.” “We observed a 60% drop in egg-laying rates, foreshadowing population decline but also other altered behaviours, such as more frequent hunching, a behaviour rarely seen in the untreated groups,” noted Justin Crocker, senior author of the study.
“Hunching” occurs when larvae curl or bend their bodies significantly, a reaction often indicating stress or discomfort. This behavior can signal serious disruptions in neurological or physiological processes, potentially caused by chemical toxicity. “On the surface, hunching may seem inconsequential, but even small changes in behaviour can impact fitness if they adversely affect feeding, mating, and migration, for example,” Crocker explained. Such shifts underline the urgency for understanding how insects interact with their surroundings and how external pressures, like chemical exposure and habitat loss, shape ecosystems.
While the connection between hunching and lower egg-laying rates remains uncertain, scientists are exploring the potential relationship between these behaviors. Still, they emphasize that larvae spending more time hunching instead of foraging may struggle to survive in the wild.
This study was a significant collaborative effort. Researchers from the Pasteur Institute, Heidelberg University Hospital, and George Washington University joined EMBL to expand the study’s scope. Together, they applied artificial intelligence to analyze behavioral changes with precise statistical insights, further testing their approach on mosquitoes and Painted Lady butterflies, both of which showed similar vulnerability patterns.
As Gandara highlights, “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.” By pinpointing chemicals with the potential to disrupt insect behavior, the research sheds light on how minimal exposure can harm insects.
As insect numbers drop, genetic diversity in these populations also suffers, a key factor for species resilience and environmental adaptation.
Crocker sums up a hopeful takeaway from the study: “The positive aspect to this work is that we have new knowledge about which chemicals can cause certain molecular changes and associated behavioural and developmental changes. By providing data on the impact and toxicity of chemicals, these assays can translate into regulatory and industrial practices that better protect human health and the environment.” These findings not only support future conservation efforts but also offer crucial insights into how chemical exposure might impact broader ecosystems.
