Global spread of butterfly disease revealed in museum collections

Butterfly collections often attract museum visitors with their vivid colors and delicate beauty. But behind the glass, these specimens hold more than just aesthetic value. A new study from the University of Georgia (UGA) shows how they can reveal patterns of disease that have gone unnoticed for decades.

The researchers focused on Ophryocystis elektroscirrha (OE), a microscopic parasite. It infects butterflies during their caterpillar stage when they eat plant leaves contaminated with spores. The infection doesn’t always kill but causes severe weakness. This can prevent butterflies from completing long migrations.

“A lot of people don’t think about butterflies as getting sick, but butterflies and other insects can be host to microbes that cause problems for them,” said Sonia Altizer, a professor in UGA’s Odum School of Ecology.

Museum butterflies reveal parasite spread

The team examined nearly 3,000 specimens from five major museums, including the Georgia Museum of Natural History.

These included butterflies collected as early as 1832. The oldest known OE infection found dated back to 1909. That’s 60 years before scientists first described the parasite in literature.

Five out of 61 butterfly species tested positive for OE. Among them were monarchs, queens, and Jamaican monarchs. This is the first report of OE infection in the Jamaican monarch.

Testing old butterflies for disease

Studying these delicate specimens required precision. The researchers used fiber swabs to collect scale samples from the butterfly’s body. The swabs were then examined under a microscope. When infected, the museum butterflies’ bodies carry visible spores of the parasite.

The experts focused on milkweed butterflies because of their worldwide presence. These butterflies eat toxic milkweed plants, which helps protect them from predators. Monarchs and queens belong to this group and are already known carriers of OE.

The study found infected butterflies from every continent except Antarctica. But the infections weren’t evenly spread. Some populations showed no infection, even within the same species.

“There were a lot of places where these species were sampled with no infection, even though there were other places where they were,” noted Altizer. “There was a lot of geographic variation within each species as to where infections were detected.”

A selective parasite

Despite OE’s global reach, only a few species seemed to suffer from it. The parasite showed up in just five butterfly species, all from the Danaus genus. This raises questions about why OE doesn’t infect other groups.

The answer may lie in parasite specialization. Spores from monarchs appeared darker and larger than spores from other butterflies. This suggests each OE strain may evolve to match its host species.

A related study led by Maria Luisa Müller-Theissen looked at how these infections crossed between monarchs and queens. Monarchs could catch OE strains from both species, while queens only reacted to their specific strains. Monarchs also showed worse symptoms than queens.

“If you put monarchs and queens side by side, the monarchs tend to outcompete the queens for food,” said Altizer. “The queens compensate for that by being more resistant to parasites and tougher in other ways.”

Museum samples and butterfly health

Museum collections offer an unmatched opportunity to study long-term ecological trends. In this study, the specimens allowed researchers to detect infection patterns over nearly 200 years.

“No one person could go all around the world and look at all these different species in a reasonable amount of time and money,” Altizer said. “But we can go to a museum and access samples from all over the world going back decades or longer and get information from these animals.”

By analyzing historical samples, scientists gain insight into butterfly health and disease evolution. This work helps explain how OE spreads and which species are most at risk.

The findings could support future butterfly conservation efforts, especially for monarchs.

Museum specimens and butterfly conservation

The research offers a deeper view into butterfly health, showing how long OE has persisted in wild populations. With climate change and habitat fragmentation on the rise, butterflies face increasing stress.

Identifying where and how OE infections spread can support global efforts to protect vulnerable species. Museum specimens, long seen as passive records of biodiversity, now serve as active tools for scientific discovery.

Ultimately, the research shows how studying the past can lead to better understanding – and protection – of our natural world.

The study was published in the journal Ecological Entomology

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