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.
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. Neonicotinoids, such as clothianidin (Bayer), are a particular hazard because, unlike most pesticides, they are soluble molecules. From soil or seed treatments they can reach nectar and are found in pollen. Neonicotinoids 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.