Preventing Diseases in Monarch Butterflies in Southwest Florida

Wild caterpillars can transmit a variety of diseases, with Nuclear Polyhedrosis Virus (NPV) being one of the most deadly.

Ophryocystis elektroscirrha (OE)

is a protozoan parasite that is ingested by caterpillars on milkweed. It spreads through microscopic spores that emerge from the wings and bodies of adult butterflies. These protozoa multiply inside the caterpillar and can cause weakness, disfigurement, and premature death.

Symptoms of OE infection can be seen in the chrysalis or butterfly. If you suspect your butterfly has a serious OE infection, releasing it will only spread the parasite to future monarchs. Infected adult monarchs harbor thousands or millions of microscopic OE spores on the outside of their bodies. When these spores are spread on milkweed eggs or leaves, monarch larvae consume them and the parasites replicate within the larvae and pupae.

Monarchs with severe OE infections may not successfully exit their pupal stage, either because they become trapped or because they are too weak to fully expand their wings. Monarchs with mild OE infections may appear normal, but they live shorter lives and cannot fly as well as healthy monarchs. Long-distance animal migrations have important consequences for infectious disease dynamics. In some cases, migration reduces pathogen transmission by eliminating infected individuals during strenuous trips and allowing animals to periodically escape from contaminated habitats.

However, human activities are now causing some migratory animals to travel shorter distances or to form sedentary (non-migratory) populations. North American monarch butterflies and a specialized protozoan parasite were studied to investigate how the loss of migratory behaviors affects the spread and evolution of pathogens. Every fall, monarchs migrate from breeding grounds in the eastern U. S. and Canada to wintering sites in central Mexico.

However, some monarchs have become non-migratory and reproduce year-round on exotic milkweed in the southern U. S.Field sampling, citizen science data, and experimental inoculations were used to quantify the prevalence of infection and the virulence of parasites among migratory and sedentary populations. The prevalence of infection was markedly higher among sedentary monarchs compared to migratory monarchs, indicating that the decline in migration increases the risk of infection. Virulence differed between parasite strains, but was similar between migratory and sedentary populations, possibly due to high gene flow or insufficient time for evolutionary divergence.

Tropical milkweed has been linked to increased transmission of Ophryocystis elektroscirrha (OE), a protozoan parasite. When OE spores infect milkweed leaves, they can be carried to the body of adult butterflies and spread the infection. Microscopic spores spread to eggs and infected larvae may not leave the pupal stage or may emerge as very weak adults. To reduce winter monarch reproduction and the risk of associated diseases, gardeners and land managers need wider access to native milkweed (which naturally age in autumn), especially in coastal areas with mild winters. The breeding of healthy monarch butterflies is based on the use of simple breeding techniques that promote the health of the monarch and, first of all, prevent monarch diseases from occurring. MonarchHealth is a project in which volunteers sample wild monarch butterflies to help track the spread of this protozoan parasite in North America.

To prevent diseases, parasites, and monarch death when releasing massive insects into your garden, it is important to clean countertops and other surfaces with bleach solution in areas where you have raised larvae or kept butterflies. Additionally, cutting plants once or twice a year can help reduce disease spores in overused plants. In conclusion, human activities that alter animal migrations may influence pathogen dynamics, with implications for wildlife conservation and future disease risks. To ensure healthy monarchs throughout their life cycle, gardeners should plant native milkweeds at appropriate distances from each other and practice regular cleaning habits.

Alexander Renaud
Alexander Renaud

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