Tropical Milkweed, Asclepias curassavica, is an evergreen perennial subshrub that can grow all year in warm, coastal climates giving butterflies a corridor through which to pass during migration. They have purple or red corollas and yellow or orange corona lobes. They attract large quantities of monarchs and are excellent in butterfly gardens.
There has been a lot of controversy and scientific studies surrounding the effects of Tropical Milkweed year-round. Throughout the winter months, Tropical Milkweed contains high levels of protozoan infection caused by Ophryocystis elektroscirrha. This parasite causes the monarch to have health deficiencies making them weak and unable to fly correctly. Most of the butterflies affected with this parasite die among emerging for their chrysalis by simply falling to the ground. Those that successfully emerge are only able to fly a short distance before they collapse.
Fortunately, there are ways to combat these protozoan infections and still plant Tropical Milkweed. As long as the plants are cut back in the fall and winter months, the parasite cannot survive and infect new butterflies.
There are several species of milkweed that grow successfully in Texas. Some of which include Antelope Horns, Green Milkweed, Butterfly Weed, Texas Milkweed, Swamp Milkweed, and Whorled Milkweed. These different species of milkweed are important to the survival of monarch butterflies. The monarchs lay their eggs on the leaves of milkweeds which serve as a habit to the caterpillar. The larvae consume the milkweed plant and sequester toxic steroids called cardenolides that help aid them in defense against predators. The toxicity from the milkweed gives the larvae a bad taste and advertises a conspicuous warning coloration. This causes predators to avoid eating the monarchs and caterpillars.
Unfortunately for the monarch butterflies, there have been a large loss of milkweed due to the usage of herbicides in fields. These "weeds" have been infesting agricultural fields and using farmland intended for crops. In order to increase crop yields, farmers have been spraying harmful pesticides to kill the milkweed causing the monarch population to decline. Without any milkweed to lay their eggs, monarchs are having trouble reproducing and traveling. The monarch population has been decreasing at an alarming rate and has reached an all time low.
Fortunately, there is still time to save the monarchs from extinction. By planting milkweed in your personal garden, we can slowly help the monarchs recover their population. Giving the monarchs a place to nest will help save the species.
If you visited the farmers' market in downtown Bryan this past Saturday you may have noticed we were selling plants to encourage people to provide habitat for the butterflies. We will be offering the plants again this fall at our Thursday market, as well as the Saturday market.