Clifton, E. H., Castrillo, L. A., Gryganskyi, A., & Hajek, A. E. (2019). A pair of native fungal pathogens drives decline of a new invasive herbivore. Proceedings of the National Academy of Sciences, 0, 201903579. https://doi.org/10.1073/pnas.1903579116
At the edge of an apple orchard in Pennsylvania, a passerby saw the bright colored wings with black spots and knew it meant trouble. If this were spotted lanternfly, the orchard was in peril. This insect, originally from Asia, feeds incessantly on more than 70 woody plants, and is a particular threat to apple and grape crops.
But on closer inspection, these adult insects seemed rather still, and rather fuzzy. Some littered the ground, unmoving. What they found can be described as a unique phenomenon called a “coepizootic” that could mean an end to the lanternfly’s reign.
“Coepizootic” (co-epi-zoo-ot-ic) is just a general term for a disease that is temporarily prevalent and widespread in a population. In this case, the disease is due to two different native fungi pathogens. When we think of fungi, “insect killer” may not immediately come to mind– but that is precisely the case with these entomopathogenic fungi.
Intrigued by this phenomenon, researchers from Cornell University sampled the deceased insects from the trees and ground. They sequenced the DNA to trace the killer fungi to two different species: Batkoa major and Beauveria bassiana.
Interestingly, the fungi divided their insect prey. B. major was responsible for killing the insects in place on the trunks of trees, whereas B. bassiana was partially to blame for the deaths on the ground.
An Effective Resistance?
Part of its power as an invasive insect comes from its lack of enemies––they escaped them when they left Asia! While spotted lanternfly continues to proliferate, seeing these two native fungi cause such mortality in the population is a special occurrence for the spotted lanternfly, and good news. The disease is evidence of biotic resistance; that the native community can keep the invasive species out on its own.
The researchers are now wondering about the potential impacts of these fungi on lanternfly populations. Can they keep the invader’s populations at a consistent, low level, or will there be population explosions and falls, like a boom-and-bust cycle? To answer this question, the researchers aim to compare these pathogens and study how they respond to different host densities.
Using pathogens to control invasive insects is a possibility, but not without its risks. Other recent research has looked into the use of insecticides for stopping the spotted lanternfly (Leach et al. 2019). The authors of this paper suggest that this chemical control could be used until a biological control, potentially these two fungi, is ready.
The Cornell researchers raised the possibility that the increased amount of the fungal pathogens could negatively affect the native insect community. Killing native insects is, of course, an outcome to be avoided. Further research on the relationship of these fungi with both the native and invasive insects will be useful in this case.
Everyday people can also play an important role in this story. Prevention and early detection of the insect can be key. So, if you see these flashy insects, report it to a local office.
Feature Image: SLF-spotted lanternfly (Lycorma delicatula) adult winged, in Pennsylvania, on July 20, 2018. USDA-ARS Photo by Stephen Ausmus. From https://www.flickr.com/photos/usdagov/43927532534