Common herbicides reduce butterfly populations by up to a third

Common herbicides reduce butterfly populations by up to a third

butterflyNew research just published by a team from Washington State University indicates that commonly used weed-killers that were previously thought to be safe can have damaging impacts on butterfly populations and threaten the survival of the rarest species.

The team from the ecotoxicology department was asked by the US Fish and Wildlife Service to examine the impacts of three commonly used herbicides on the larvae of the highly endangered Lange’s metalmark. The three herbicides: triclopyr, sethoxydim and imazapyr, are regularly used to maintain the last habitat of the butterfly during conservation measures.

Butterfly larvae exposed to common herbicides led to reduced adult populations.

Because of the highly threaten nature of the Lange’s metalmark – now down to as low as 45 individuals compared to 25,000 over 50 years ago – the team undertook tests on the Behr’s metalmark butterfly.

What the researchers found was of concern considering that these herbicides are normally considered safe for use. When the larvae were exposed to the herbicides the adult butterfly  populations numbers dropped by between 25% and 30%.

John Stark, an ecotoxicologist and director of the WSU Puyallup Research and Extension Center, remarked, “In a small population of endangered animals any kind of reduction like that is going to be a problem.“ 

First study looking at impacts of herbicides on butterflies.

The study, funded by the Fish and Wildlife Service and published in the journal Environmental Pollution, is one of the first to document the negative effects of weed-killers on butterflies. Previous other studies though have shown herbicides can negatively impact on animal life, even though they are designed to act against plants. 

Each of the three herbicides in the Stark study operate differently, leading the researchers to think butterflies are being affected by inert ingredients or an effect on the butterflies’ food source.

Only 1 of the 3 herbicides still permitted to be sold in the UK.

In the UK only one of the three studied herbicide types is still on sale for use.

Imazapyr was withdrawn from sale in the UK in 2003 after new European herbicide regulations were introduced. The chemical is a non-selective herbicide and at the time of use it was considered to be safe for use in the environment. It is considered to have low toxicity to both aquatic and terrestrial wildlife and minimal impacts on the environment.

Sethoxydim was also removed from sale in the UK following the update of European herbicide approval in 2003. The herbicide targets annual and perennial grasses and is often used to protect broad leaved crops such as beets.

Triclopyr is still in widespread use today in the UK both in industrial products and domestic garden products. It targets broadleaved plants such as docks, brambles and nettles. It is also widely used in forestry practices to prevent unwanted standing coppice and shrubs. The herbicide is considered same for the environment and of low toxicity to terrestrial animals. It is also considered to be non-toxic to bees and low toxicity to birds.

First introduced in 1979 triclopyr is regularly used over large-scale landscapes such as golf-courses and roadside verges for maintaining grasses. The herbicides containing triclopyr are made by Scotts Miracle-Gro Company and Dow AgroSciences. 

Triclopyr marketing to domestic consumers go under product names such as:

  • Weed-B-Gone, 
  • MAX Poison Ivy and Tough Brush Killer,
  • Access,
  • Crossbow,
  • Confront
  • Pathfinder II,
  • Turflon,
  • Release,
  • Garlon 3A,
  • and Garlon 4.

It is also worth reading the labels of other products to determine if they contain triclopyr as brand names, ingredients and marketing changes regularly.

External sites:

Effects of herbicides on Behr’s metalmark butterfly, a surrogate species for the endangered butterfly, Lange’s metalmark.

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One thought on “Common herbicides reduce butterfly populations by up to a third

  1. Amazing that the Langes Metalmark butterfly was down to 45 and here they were using herbicides on the area, the very thing that was part of the diminishing population.

    Thanks for publishing this. I avoid herbicides as I am concerned about those it comes into contact with. Whether that be children, the animals in our yard, wildlife or insects. I am going to mention this post on my blog

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