Study finds use of pesticide to suppress hemlock woolly adelgid does not pose risk to aquatic macroinvertebrate communities

Hemlock woolly adelgid [Adelges tsugae (Annand)] is an invasive insect pest of eastern hemlock [Tsugacanadensis (L.) Carrièr)] and Carolina hemlock (Tsuga caroliniana Engelmann). In some forests, hemlocks fill an ecological niche that cannot be filled by other native evergreen trees, so control of the hemlock wooly adelgid is important.

The insecticide imidacloprid has been widely used for hemlock woolly adelgid suppression. However, imidacloprid is a neonicotinoid, a class of insecticide that has received considerable attention in the media due to its reported impacts on non-target organisms, including several aquatic invertebrates.

Recently, a group of researchers assessed aquatic macroinvertebrate communities in nine streams in Great Smoky Mountains National Park. The streams flow through hemlock conservation areas where imidacloprid has been used for hemlock woolly adelgid suppression.

In these areas, imidacloprid has been applied as a soil drench and to tree trunks in multi-application (up to six applications) treatment cycles. The researchers detected imidacloprid residues in six of the nine streams sampled up to 42 months after the final application.

The researchers also conducted “aquatic macroinvertebrate multihabitat bioassessments” in the nine streams by sampling at a site downstream of the imidacloprid-treated area and a control site upstream of the conservation area. They found that downstream sites were typified by rich and diverse aquatic macroinvertebrate communities and concluded that use of imidacloprid has not had detrimental impacts on aquatic macroinvertebrates.

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Benton, E.P., J.F. Grant, R.J. Nichols, R.J. Webster, J.S. Schwartz, and J.K. Bailey. 2017. Risk assessment of imidacloprid use in forest settings on the aquatic macroinvertebrate community. Environmental Toxicology and Chemistry 36:3108-3119.