posted about a monarch butterfly deformed upon emerging from its pupa. I went on about how maybe the winter timing of its emergence had something to do with its deformity or difficulty eclosing.
This was clearly incorrect as the butterflies, and all of the caterpillars mentioned in that post as well, was infected with the OE parasite (Ophryocystis elektroscirrha). The caterpillars ingest the spores of the parasite as they feed, which have been deposited there by their infected mother as she laid the eggs.
Turns out that winter 2012 was the peak of our OE infestation. The emerging adults were so heavily infested they were unable to mate and reproduce, resulting in population crash. I also removed all of the milkweed in January 2013 in the interest of preventing the spread of the parasite. 2013 there were zero monarchs about the estate. At the house across the street, a lush stand of milkweed started up mid year and this adult emerged apparently healthy.
signs of infestation although in light infestions there may be no indication short of microscopic examination.