Friday Cat-erpillar Blogging: Monarchs and Disease

Monarch butterflies are protected from predation by birds due to the toxic chemicals they sequester from their milkweed host plants. The interactions between birds, monarchs and chemicals in milkweed are well known. Lesser known are interactions with the protozoan parasite, Ophryocystis elektroscirrha, that can infect monarch butterflies and shorten their lifespan. The parasites are passed from mother to egg. Studies by Lefèvre and colleagues* have shown that the parasites produce fewer spores and cause less harm to larvae feeding on milkweed species with high cardenolide content, such as the tropical milkweed Asclepias curassavica, than on species with low cardenolide content such as the swamp milkweed, Asclepias incarnata.

Parasites can have an important role in host plant choice. Butterflies that choose a suitable host plant can survive the parasite. On plants that are otherwise suitable for monarch growth and development, monarchs may succumb to the protozoan parasite. These interactions further limit host plant range for many insects.

Monarch Larva on Milkweed Leaf

*(Lefèvre, T., Oliver, L., Hunter, M.D. & de Roode, J.C. (2010) Evidence for trans-generational medication in nature. Ecology Letters, 13, 1485–1493)

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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