This research connects infectious disease dynamics to ecosystem health by examining how climate change affects the biocontrol of invasive species. The fungal pathogen Entomophaga maimaiga has kept spongy moth populations in check, much like how infectious diseases are controlled in humans. Using disease models designed for humans, researchers analyze how environmental changes impact the spread of pathogens in insect populations.
Spongy moths (Lymantria dispar), notorious for their destructive impact on North American forests, have long been a concern for forest managers and ecologists. The moths, introduced to North America in 1869, have caused significant damage to hardwood forests, particularly attacking oak trees. This has contributed to a phenomenon known as “oak decline,” where oaks are being replaced by more resilient but less ecologically valuable species like maples. In 1989, a natural biocontrol, E maimaiga, a fungal pathogen, was introduced and helped to suppress spongy moth populations for nearly three decades.
In our interview with Greg Dwyer, PhD, professor in the department of ecology and evolution at the University of Chicago, we explored the intersection of climate change, invasive species, and ecosystem health. Dwyer, a quantitative ecologist who uses mathematical models to study disease dynamics in insect populations, discussed the significance of the fungal biocontrol of the invasive spongy moth. He explained the moth’s destructive impact “Spongy moth is an insect. It’s a moth. It has a caterpillar that feeds on many different species of trees, and it was accidentally introduced into North America in 1869… and since then, they’ve spread through much of North America, and they have a terrible effect on hardwood forests, which means forests that have broadleaf trees in them. They especially attack oak trees, and they are one of the contributing factors in oak decline, which is the replacement of oaks by maples in hardwood forests.”
For nearly 30 years, E maimaiga kept the spongy moths in check. But Dwyer warns that climate change is now threatening the effectiveness of this natural biocontrol. “Spongy moths caused terrible damage in North America for decades, and then in 1989 the fungal disease was introduced… it spread very rapidly and wiped out spongy moth populations. And the fungus effectively suppressed spongy moth populations for almost 30 years, and this has allowed oak forests to rebound to some extent from the previous decades of destruction.”
Dwyer points out the conditions E maimaiga thrives in, “The fungal disease needs cool, moist conditions to spread. And as temperatures rise and relative humidity falls across the northeastern US and southeastern Canada, the fungal disease is having a difficult time spreading, and as a result, spongy moth populations are beginning to rebound.”
This shift in the dynamics between the spongy moth and its biocontrol could have far-reaching consequences for forest ecosystems. Dwyer emphasizes the broader ecological importance of oak trees, “Oaks are a very important component of hardwood forests, partly because they support more insects and a wider variety of insects than other types of trees, and that supports many different species of perching birds. And so, perching birds rely on there being a high density of oaks. Also, oaks produce acorns, whereas maple trees, their seeds are these little keys, the little helicopter things that fall off the trees in the fall. Acorns are much more nutritious, and so they support large populations of wild turkeys and white-tailed deer, which also feed on acorns, and squirrels and chipmunks, many different species in the forest. As oaks decline, our forests will lose diversity, just because there will be a lower frequency of oaks, but also because all these other species depend on oaks for their living.”
The repercussions of this shift in the balance of species could be felt throughout the ecosystem, affecting plant and animal populations that depend on oak-dominated forests. According to Dwyer, the broader impact of the decline of the fungal disease is far-reaching, “The decline of the fungal disease will have these impacts that radiate through the forest.”
In their study, Dwyer and his colleagues utilized mathematical models originally designed for studying human infectious diseases, such as measles and COVID-19, to understand the spread of insect diseases. “A surprising feature of our study, is that we use mathematical models that were originally developed to describe the spread of human diseases—human infectious diseases like measles or COVID or what have you. But they work very, very well for insect diseases as well, which are also directly transmitted. The disease jumps from insect to insect. It’s an example of how mathematical and computing developments in one area can be of great use in another area of science.”
This cross-disciplinary approach also offers insight into how climate change may influence the spread of other diseases, particularly fungal infections and viruses. Dwyer highlights the importance of connecting data with models to project future disease dynamics under changing climate conditions, “One of the things that we learned is that in order to project how climate change will affect a disease, we need to have a very close connection between models and data. So, there are parameters in our computer models that can only be estimated by collecting very detailed data in the field.”
As climate change disrupts the balance between pests, pathogens, and their natural controls, Dwyer’s work highlights the need to understand these shifts, not only for forest health but also for public health, as these changes can ripple through ecosystems, affecting food chains and biodiversity.
