South Florida’s butterflies have become the unintended victim of insecticide control, according to FIU researchers.

A five-year study by scientists in the FIU Ecotoxicology and Risk Assessment Lab has found that exposure to naled, permethrin and dichlorvos — insecticides sprayed locally for mosquito control — are acutely toxic with some species being more sensitive than others.

“Changes in butterfly populations that occur as a result of natural factors are difficult to control and manage,” said Gary Rand, director of the Ecotoxicology and Risk Assessment Lab and professor of environmental studies. “Human factors, like our use of insecticides, can certainly be monitored and managed more effectively.”

Researchers studied the abundance and diversity of butterfly populations, including common buckeye, white peacock, atala hairstreak, painted lady and zebra longwing. The butterflies were most directly affected by insecticides sprayed in the air and ground, but they were also significantly exposed to the chemicals by eating contaminated plant leaves as caterpillars. The researchers found naled was most acutely toxic when ingested. The studies were funded by the U.S. Fish and Wildlife Service and were published in Environmental Toxicology and Chemistry; Science of the Total Environment; and Chemosphere.

“These results are based only on ingestion and single chemical doses,” Rand said. “It doesn’t include other typical exposure scenarios that may occur in the environment, where the organisms may be exposed via environmental drift and to multiple or continuous exposures.”

The Environmental Protection Agency (EPA) lists the insecticides naled, permethrin and dichlorvos as highly toxic to aquatic organisms and honeybees and relies on honeybees to test the effects of insecticides on unintended targets. According to the researchers, butterflies, with their much larger surface areas, are at greater risk of exposure than the smaller honeybee. They recommend using butterflies as potential test organisms when testing the effects of pesticides on non-target organisms.