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Monarch butterfly (Danaus plexipus) caterpillar feeding on butterflyweed (Asclepias tuberosa), a relative of milkweed. Photo: Martin LaBar via Flickr (CC BY-NC).
Monarch butterfly (Danaus plexipus) caterpillar feeding on butterflyweed (Asclepias tuberosa), a relative of milkweed. Photo: Martin LaBar via Flickr (CC BY-NC).
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Neonicotinoid link to Monarch butterfly decline

Jonathan Latham

9th April 2015

Monarch caterpillars are vulnerable to neonicotinoid toxicity at concentrations as low as 1 part per billion, writes Jonathan Latham, and that makes them vulnerable to residues from commercial crops - and even more so from horticultural use in plant nurseries!

Clothianidin can have effects on monarch caterpillars at doses as low as 1 part per billion. The effects seen in their experiments were on caterpillar size, caterpillar weight, and caterpillar survival.

USDA researchers have identified the neonicotinoid insecticide clothianidin as a likely contributor to monarch butterfly declines in North America.

The USDA research is published in the journal Science of Nature and was published online on 3rd April (Pecenka and Lundgren 2015).  (ISN has had hacking problems, again. If this page is unavailable to you, thank the chemical industry, and please try later)

Monarch butterfly populations (Danaus Plexippus) have declined precipitously in North America in the last twenty years. This decline has commonly been linked to loss of milkweeds (Asclepias species) from farmer's fields.

Monarch caterpillars are dependent on milkweeds. The ability of farmers to kill them with the Monsanto herbicide Roundup (glyphosate) has therefore led to this herbicide being considered as a major contributor to the decline of the monarch butterfly.

However, industrial farming methods include other known or potential causes of monarch disappearances. One of these is the known toxicity of Bt insecticides found in GMO crops.

For instance, in 2006 pollen from Syngenta's BT176 corn (no longer on the US market) was shown to have a lethal dose of 14 pollen grains towards caterpillars of European Swallowtail butterflies.

Pollen from GMO crops falls on the milkweeds where monarchs feed and individual maize plants produce millions of pollen grains.

'Neonic' pesticides - toxic to caterpillars at 1 part per billion

Neonicotinoids have been strongly implicated in pollinator declines worldwide, as shown by a report from a task force of the International Union of Nature Conservation based in Switzerland.

These pesticides, such as clothianidin (Bayer), are a particular hazard because, unlike most pesticides, they are water-soluble molecules.

From soil or seed treatments they can reach nectar and are found in pollen. They are now the most widely used pesticides in the world (Goulson 2013). Up to now there has been negligible research on the effects of neonicotinoids on butterflies and this new research is therefore the first to link neonicotinoids to the survival and reproduction of any butterfly.

In their experiments the USDA researchers showed that clothianidin can have effects on monarch caterpillars at doses as low as 1 part per billion. The effects seen in their experiments were on caterpillar size, caterpillar weight, and caterpillar survival. The lethal dose (LC50) they found to be 15 parts per billion.

The caterpillars in their experiments were exposed to clothianidin-treated food for only 36 hours, however. The researchers therefore noted that in agricultural environments caterpillar exposure would likely be greater than in their experiments. Furthermore, that butterfly caterpillars would be exposed in nature to other pesticides, including other neonicotinoids.

In sampling experiments from agricultural areas in South Dakota the researchers found that milkweeds had on average over 1ppb clothianidin. On this basis the USDA researchers concluded that "neonicotinoids could negatively affect larval monarch populations."

This new report is therefore the first to link neonicotinoids to monarch butterfly survival and reproduction. Neonicotinoids are neurotoxins that are partially banned in the EU.

And an even greater hazard in horticulture

Now a new paper in Plos ONE shows that far greater concentration of pesticide are achieved in the plant nursery and horticulture industry, where plants are routinely treated with the neonicotinoid Imidaclopri - and as much as 300mg of active ingredient may be used in a single large pot.

This means that domestic gardens - often considered a 'haven' for wildlife species that can no longer survive in chemical-drenched, GMO-occupied farmland - can present an even great toxic hazard. Most gardeners will never even know that their commercial plant purchases are helping to wipe out the biodiversity they are trying to save.

"Translocation of imidacloprid from soil (300 mg AI) to flowers of Asclepias curassavica resulted in 6,030 ppb in 1X and 10,400 ppb in 2X treatments, which are similar to imidacloprid residues found in another plant species we studied", the paper by Dr. Vera Krischik and colleagues reports.

"A second imidacloprid soil application 7 months later resulted in 21,000 ppb in 1X and 45,000 ppb in 2X treatments. Consequently, greenhouse/nursery use of imidacloprid applied to flowering plants can result in 793 to 1,368 times higher concentration compared to an imidacloprid seed treatment (7.6 ppb pollen in seed- treated canola), where most research has focused.

"These higher imidacloprid levels caused significant mortality in both 1X and 2X treatments in 3 lady beetle species, Coleomegilla maculata, Harmonia axyridis, and Hippodamia convergens, but not a fourth species, Coccinella septempunctata. Adult survival were not reduced for monarch, Danaus plexippus and painted lady, Vanessa cardui, butterflies, but larval survival was significantly reduced.

"The use of the neonicotinoid imidacloprid at greenhouse/nursery rates reduced survival of beneficial insects feeding on pollen and nectar and is incompatible with the principles of Integrated Pest Management."

Using toxins to kill pests runs contrary to all biological understanding

"These results are very worrisome, but it is also crucial not to get lost in the specifics of chemical toxicology and individual species declines", says Allison Wilson, Science Director of the Bioscience Resource Project, a non-profit public interest science organization.

"Industrial agriculture is a lethal combination of methods that is causing the extinction of thousands of species worldwide. It is affecting birds, amphibians, bats and other pollinators besides butterflies. Many ecosystems are staring down the barrel."

"The saddest irony is that, though industrial agriculture experts call their methods 'scientific', using toxins to kill pests runs contrary to all biological understanding, including the sciences of ecology, of evolution, and of complex systems.

"The proof of this is that the very best results in all of agriculture come from farming methods that reject all industrial inputs. Agribusiness would very much like that not to be known.

"The best news is that there is a simple way to transfer to sustainable agricultural methods: remove the subsidies for industrial farming."

 


 

Jonathan Latham is editor of Independent Science News.

This article was originally published on Independent Science News. It has been extended by The Ecologist to include new information about the vera Krischick paper.

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