Asclepias curassavica, commonly known as tropical milkweed, has become a popular choice in gardens and landscapes due to its vibrant flowers and ability to attract butterflies, including monarchs. However, there are concerns about the potential negative impacts of this plant on monarch populations.
One of the main issues with tropical milkweed is its prolonged flowering period, which can last throughout the year in warmer climates. While this may seem like a positive attribute, it can actually disrupt the natural migration patterns of monarch butterflies.
Monarchs rely on environmental cues, such as day length, to trigger their migratory behavior. However, when they encounter tropical milkweed that continues to produce flowers, it can confuse their internal navigation system. Instead of continuing their journey to their overwintering grounds in Mexico, some monarchs may decide to stay and breed on the readily available tropical milkweed.
This extended breeding period can have detrimental effects on monarch populations. It can lead to an increase in the prevalence of a parasitic protozoan called Ophryocystis elektroscirrha (OE). OE can be transmitted from infected adult butterflies to their offspring, and high parasite loads can weaken monarchs, making them more susceptible to diseases and reducing their chances of survival.
Furthermore, the presence of tropical milkweed throughout the year can create a continuous breeding habitat for monarchs, which may result in higher population densities than would occur naturally. This can put additional pressure on limited resources, such as nectar plants and milkweed availability, leading to competition among monarchs and potentially impacting their overall health and reproductive success.
It is worth noting that not all regions are equally affected by the negative impacts of tropical milkweed. In areas where monarchs do not overwinter, such as southern Florida and parts of southern Texas, year-round availability of milkweed may not disrupt migration patterns as significantly. However, in regions where monarchs rely on migratory behavior to complete their life cycle, such as the central and eastern parts of North America, the presence of tropical milkweed can be problematic.
To mitigate the potential negative impacts of tropical milkweed on monarchs, it is recommended to consider planting native milkweed species instead. Native milkweeds naturally go dormant during the winter months, aligning with the natural life cycle of monarchs and reducing the risk of prolonged breeding and disease transmission.
While tropical milkweed may be visually appealing and attract butterflies, including monarchs, its year-round availability can disrupt monarch migration patterns and contribute to the spread of diseases like OE. It is important to be aware of these potential impacts and consider planting native milkweed species to support monarch conservation efforts.
