While there are a number of milkweed varieties that one can grow in Missouri, many of them don’t last very long and could be expensive if you want to grow a large patch. Asclepias curassavica is an annual variety that blooms all summer long and is both a great nectar plant and host plant. There have been a number of questions about it so I thought I’d review some of the research.
Dr. Jeffrey Glassberg who is the director of NABA, the North American Butterfly Association has written a long article on this subject. He refutes the arguments against tropical milkweed in this article.
Ophryocystis elektroscirrha, or OE is a disease that Monarchs get and might kill them. The problem is theorized that OE will last over the winter on plants in southern states where the plants will over-winter. That’s not a problem in Missouri since all our annual milkweed plants die with the first frost. I also start my milkweed from seed. While OE is a problem in Florida and some southern states, it is not a problem in Missouri since there are no plants which over-winter with the disease.
Dr. Lincoln Brower says this, “Another problem with establishing what becomes a continuously breeding population of monarchs is that the incidence of the protozoan parasitic disease (Ophryocystis elektroscirrha) increases with time. If the diseased individuals then somehow end up breeding with or joining the overwintering clusters of monarchs, then the incidence of the disease will very likely rise with detrimental effects on the migratory monarch populations.” Professor Sonia Altizer at the University of Georgia, who is the World expert on O. e., agrees with me.
Tom – while this might apply to southern states, it does not apply to Missouri or northern states.
Does Curassavica cause Monarchs to leave Diapause?
Diapause is the period of time when the last generation of Monarchs stop maturing sexually. Although they look like normal Monarchs, “they won’t mate or lay eggs until the following spring.” They need to use all their energy for their flight to Mexico and their hibernation while there.
There is a good article from the University of Minnesota’s Monarch Lab which says from their testing that “Environmental factors signaling the onset of unfavorable conditions are involved in triggering this physiological response. These factors include day length, temperature, and host plant quality.”Here is their full report.
In my experience over the last fifteen years, while Monarchs do visit my garden in the fall and fuel up on tropical milkweed nectar, they generally don’t stay more than a day or two at the most and when a cool front passes through they are all gone. Also when we tag Monarchs in the fall, they will all be gone usually by the next day.