DRESDEN, Ont. — The monarch butterfly recently joined a growing list of non-target insects that may be affected by neonicotinoid seed treatments.
“Our study was intended to point out that they are potentially a contributor to the decline of the monarch and that more work needs to be done,” said Jonathon Lundgren, a scientist with the U.S. Department of Agriculture’s Agricultural Research Service.
Lundgren, together with graduate student Jacob Pecenka, published their findings in the April edition of The Science of Nature.
The researchers confirmed the lethal and non-lethal toxicity of clothianidin to monarch larvae in the laboratory and also tested common milkweed in 18 roadside ditch locations adjacent to corn fields for presence of the insecticide.
The samples were taken only in South Dakota, and Lundgren said further study covering a wider geographic area is warranted. However, he also feels practices in the region are similar to those throughout the U.S. corn belt.
Adverse impacts were observed when larvae fed on milkweed containing as little as one part per billion of clothianidin. The average content of the milkweed that was tested averaged 1.14 and as much as four p.p.b. were recorded.
“The prolonged presence of clothianidin indicates that monarch larvae are likely to be exposed to clothianidin through their larval lives and that the 36 hour exposure event in our toxicity assay is an underestimate of field exposures.”
Reductions in monarch butterfly populations have also been linked to the loss of habitat in agricultural regions.