Insecticide Sends Caddisflies Away from Protective Cases

As animal architects, caddisflies defend themselves from predators and environmental extremes through the construction of a protective enclosure. A new study explores the unexpected negative effects on caddisflies of accidental exposure to the agricultural insecticide esfenvalerate, including case abandonment and decreased chance of survival. The study is published in the latest issue of Environmental Toxicology and Chemistry.

Synthetic pyrethroids, like esfenvalerate, affect nerve activity. For instance, they can cause twitching, muscle spasms, and burning or itching sensations in nontarget aquatic organisms. Synthetic pyrethroid use is increasing in both agricultural and urban settings. This study validates concerns that such use may pose an unexpected risk to nontarget aquatic organisms.

The researchers found that exposure to sublethal concentrations of this chemical induced behavioral responses including case abandonment by caddisflies. Once deprived of a case, a caddisfly larva can rebuild an entirely new case, but this is an energetically costly process. Adults reared from larvae that were forced to rebuild cases had small wings and bodies when compared with adults reared from larvae that did not need to rebuild.

The study's researchers found that less than 20 percent of exposed insects rebuilt their cases. Cases that were rebuilt were disorganized and were weaker than cases built by unexposed larvae. Larvae living in rebuilt cases and larvae without cases were significantly more susceptible to predation than those in original cases. Overall, the researchers concluded that small behavioral responses had profound consequences for the survival of the caddisflies and thus could have effects on stream ecosystems of which these animal architects are an important component.

Environmental Toxicology and Chemistry is the monthly journal of the Society of Environmental Toxicology and Chemistry.

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