As winters get warmer, Asclepias curassavica, the only milkweed species commercially available, is less likely to die back in winter. Some scientists hypothesize that A. curassavica entices Monarchs to forego migration and winter in the U.S. This could create an unhealthy hotbed of lingering OE spores for caterpillars and butterflies that remain in the local area.
Since the spores transfer from creature to creature via physical contact with each other or the plants on which they rest or eat, scientists worry that local OE-infested Monarchs will infect and breed with populations that are passing through, possibly jeopardizing the migration.
The situation exacerbates an already serious decline in the Monarch migration. Drought, genetically modified crops, late summer wildfires, and generally inhospitable conditions pose multiple threats to Monarchs and their migration. It’s likely that 2012 will be the worst year, numbers wise, in Monarch butterfly migration history since records have been kept.
“Monarchs are famous for this migration so when we see what appears to be a break in their migratory pattern, we want to know why and what the implications are,” said Satterfield.