Nature's defense against the invasive spongy moth is fading

Hotter, drier North American climates will curtail the growth of a critical fungus used to keep the invasive spongy moth (Lymantria dispar) in check, according to computer models recently devised by scientists.

The research, led by the University of Chicago and the Argonne National Laboratory, highlights the interconnected nature of climate change impacts by showing how higher temperatures can ripple through ecosystems and alter species interactions in unexpected ways.

Greg Dwyer is a professor of ecology and evolution at UChicago and senior author of the study. 

“The vast majority of previous climate change studies look at individual organisms, but a small amount of climate change can have a big effect when you compound it across multiple species,” said Dwyer. 

“So, computer models are crucial for understanding the effects of climate change on species interactions.”

Spongy moth: A destructive invader

Introduced to North America in 1869, the spongy moth originates from Europe.

Female moths deposit their eggs on various surfaces – such as branches, stacked firewood, and outdoor furniture – which people can inadvertently transport far beyond the moth’s initial release site in Massachusetts. 

Once hatched, the caterpillars voraciously consume the leaves of hardwood forests, particularly oaks, leading to large-scale defoliation and significant tree mortality.

Fungi vs. forest invaders

Relief arrived in 1989, when the fungus Entomophaga maimaiga began to spread among spongy moth populations. 

While it’s not certain how or when this non-native fungus arrived in North America – whether intentionally introduced for control or accidentally imported – the fungus effectively curbed moth outbreaks for decades. 

Another pathogen, the nucleopolyhedrovirus (NPV), also helps keep spongy moth numbers down, but it requires large moth populations to spread efficiently.

The E. maimaiga fungus, in contrast, can develop in small moth populations before major destruction sets in, provided that conditions are cool and moist.

How warming affects moth-fungus dynamics

As part of their study, Dwyer and his colleagues collaborated with atmospheric scientists Jiali Wang and Rao Kotamarthi from the Argonne National Laboratory to integrate advanced climate modeling into existing spongy moth population models. 

By refining large-scale climate data to capture regional differences in temperature and precipitation, the research team could project how changing environments affect the interplay of spongy moths, their predators, and pathogens like E. maimaiga.

The simulations revealed that rising temperatures and drier weather reduce the infection rates of E. maimaiga, resulting in fewer moth deaths.

As spongy moths become more likely to survive and reproduce, they cause more extensive defoliation. 

Multiplication of the spongy moth

“Even small reductions in mortality rate for the moths lead to big increases in defoliation,” Dwyer explained.

“If they don’t get killed off when they’re at low density one year, then the next year they’ll be back at higher density. You get this multiplication process going on.”

Recent seasonal trends have already hinted at what the future might hold. Below-average rainfall paired with above-average temperatures helped spur significant moth outbreaks, earlier than the researchers expected. 

“Our projections were pessimistic, but probably not pessimistic enough. It’s very concerning,” said Dwyer.

The domino effect of climate change

The study highlights the importance of treating species interactions as dynamic systems, where even slight changes in temperature or humidity can cascade across multiple organisms. 

In this case, the spongy moth, the fungus that infects it, and the overall forest ecosystem are interlinked. As warmer, drier conditions limit E. maimaiga, spongy moth numbers surge, ultimately threatening forest health and stability.

The spongy moth’s destructive capacity poses a financial burden as well, given the expensive efforts needed to manage infestations and the losses in timber and ecosystem services resulting from tree deaths.

Controlling spongy moth populations 

By drawing attention to the vulnerability of E. maimaiga under climate change, the study suggests that forest managers and policymakers might need alternative or supplemental approaches to control spongy moth populations. 

In addition, other species could be affected in similarly indirect ways – a warning that climate change can reshape ecological communities through multiple layers of interaction.

In the future, the team hopes to test its model’s predictions in real-world settings and refine it to factor in additional complexities, such as geographic variations in forest composition and predator species. 

Preserving the health of our forests 

By deepening our understanding of how climate change influences species relationships, researchers can help guide effective solutions for preserving forest health and maintaining biodiversity.

Overall, the research highlights a broader truth about ecological management in a changing world: when one piece of the puzzle shifts, the entire system can behave in unexpected ways. 

As Dwyer put it, “a small amount of climate change can have a big effect when you compound it across multiple species,” and the spongy moth’s changing fate exemplifies that message.

The study is published in the journal Nature Climate Change.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–