Efficacy and Nontarget Effects of a Spinosad-Based Larvicide in Minnesota Vernal Pools and Cattail Marshes

ABSTRACT Larvicides that contain spinosad, a bacterial metabolite, are used to control mosquitoes in diverse aquatic habitats. These same habitats are home to other invertebrates, including Crustacea—fairy shrimp, isopods, and amphipods—and mollusks—fingernail clams and freshwater snails. A double-blind study evaluated the effects of Natular® G, a granular treatment containing spinosad, on spring Aedes spp. and nontarget invertebrates in vernal wetlands. Within 14 days after application, Natular G controlled larvae of spring Aedes by 53–84%, depending on species, but had no significant effects on numbers of fairy shrimp, fingernail clams, or freshwater snails. A second double-blind study evaluated effects on Coquillettidia perturbans and nontarget isopods and amphipods in cattail marshes. Treatment reduced emergence of Cq. perturbans by 25% but did not change numbers of isopods or amphipods. The 2 experiments indicate Natular G could be effective against spring Aedes in vernal wetlands, less so against Cq. perturbans in cattail marshes, and yet pose minimal risk to crustaceans and mollusks in either vernal wetlands or cattail marshes.