(Tom: This is tragic. Please support any petition or other attempt to curb the use of pesticieds and eschew their use yourself. Investigate companion planting and other means of more sustainable agriculture.)
New evidence identifies 64 pesticide residues in milkweed, the main food for monarch butterflies in the west. Milkweed samples from all of the locations studied in California’s Central Valley were contaminated with pesticides, sometimes at levels harmful to monarchs and other insects.
The study raises alarms for remaining western monarchs, a population already at a precariously small size. Over the last few decades their overwintering numbers have plummeted to less than 1% of the population size than in the 1980s – which is a critically low level.
Monarch toxicity data is only available for four of the 64 pesticides found, and even with this limited data, 32% of the samples contained pesticide levels known to be lethal to monarchs, according to a study released today in Frontiers in Ecology and Evolution.
https://www.unr.edu/nevada-today/news/2020/butterflies-and-pesticides