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Monarch Health Troubles - Sep 12, 2011

by Kelle Hartman, Educator, Green Bay Botanical Garden

Not even the insect world is free of health problems.  One of the newest causes for concern is a parasite known as Ophryocystis ecektroscirrha (or OE) that infects monarch butterflies.  Though this parasite is not new, OE was first discovered in the late 1960’s, the monarch populations in the Midwestern and Eastern United States are not heavily infected so it’s been easy to miss.  And unless you’re raising monarch caterpillars at home, you probably won’t notice whether a caterpillar is infected.

The life of the parasite OE is closely related to the monarch life cycle.  When an infected female lays her eggs, dormant spores on the outside of her abdomen are scattered on the egg.  When the egg hatches, the first thing the tiny caterpillar eats is its eggshell, and the OE spores with it.  As the caterpillar’s body begins to digest the spores, the chemicals in the stomach break open the spores and the parasites are released.  They then divide within the caterpillar’s body and their numbers multiply.

The most damage to the monarch occurs during the pupa stage, or chrysalis.  Just before the butterfly will emerge from its chrysalis, OE spores form.  Creating spores allows the OE to survive outside the monarch’s body.  If the butterfly emerges, the infected adults can be smaller than healthy adults, may loose weight more quickly, and may be unable to fly as far as unaffected adults.  The butterfly is also covered in spores which females can pass on to its eggs or males can pass onto females while mating.  In severe cases, they adult butterfly may emerge deformed and quickly die or may never emerge from the chrysalis at all.

The Butterfly House in the children’s garden has not avoided the problems of OE this summer.  While we usually raise about two dozen caterpillars each summer with no problems, we’ve had an increase in the number of monarch caterpillars that have died in the chrysalis stage.  Next summer we’ll be raising our caterpillars in individual containers to help prevent the spread of the parasite and placing them into the Butterfly House as chrysalises.  We look forward to a larger, healthier batch of monarchs next summer!

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