Disease as well as climate change have been suggested, but milkweed got a big boost due to the introduction of widespread farming by European settlers, but this was reversed by improvements in weed control. I think that we only had reliable counts on Monarchs since the 1990s, but I also have witnessed the decline, and more recently an increase which I attribute to increased plantings of milkweed. Time will tell, but we are doing what we can on our place. It is really no hardship to add milkweed to our habitat improvement activities, along with other flowering plants. We saw quite a few giant swallowtails this year which was nice, but I am not sure where they were finding their larval host plants.
