A new study finds a correlation between the aerial spraying of pesticides to kill mosquitoes and an increased risk of developmental delays and autism among kids. In the new findings, presented at the Pediatric Academic Societies 2016 meeting, researchers looked at the rates of autism and developmental delays from eight zip codes in a region of New York that is exposed to yearly airplane pesticide spraying to prevent mosquito-borne disease like eastern equine encephalitis virus. They compared those to the rates in 16 zip codes where the pesticide spraying doesn't happen. They controlled for factors like poverty and gender variation across the zip codes. The authors report that kids living in zip codes where the spraying was done each summer had around a 25% higher risk of an autism diagnosis or developmental problems compared to kids living in areas without the aerial spraying. "Several studies have previously reported links between pesticide and autism risk," says Dr. Steve Hicks, an assistant professor of pediatrics at Penn State College of Medicine in an email to TIME. "Our data suggests the way in which pesticides are applied might play some role. Studies of pesticides in animal models show they can affect certain neurotransmitters in the brain, but their exact molecular effects on brain development are still being explored."