Destructive plant pest thwarted by two native fungi
By Krishna Ramanujan
Cornell-led research reports that two local fungal pathogens could potentially curb an invasive insect that has New York vineyard owners on edge.
The spotted lanternfly feeds on more than 70 plant species, including grape vines and apple trees.
Now, the paper, “A pair of native fungal pathogens drives decline of a new invasive herbivore,” led by Eric Clifton, a postdoctoral researcher in the lab of Cornell professor of entomology and co-author Ann Hajek, describes how two unrelated fungi, Batkoa major and Beauveria bassiana, have been decimating spotted lanternfly (Lycorma delicatula) populations near Reading, Pennsylvania.
“The finding is important because these naturally occurring pathogens could be used to develop methods for more environmentally-friendly control of this damaging invader,” Hajek said.
“It’s a great example of how a major new invasive herbivore can be suppressed by native pathogens,” Clifton said. “Nobody stepped in to do this; it all happened naturally.”
Native to China, Taiwan and Vietnam, the spotted lanternfly was first discovered in southeastern Pennsylvania in 2014 and has spread to seven more states. Adult insects occasionally have been sighted in New York, but there are no signs yet of large populations. Entomologists and growers believe it’s just a matter of time before spotted lanternflies settle in New York, which boasts a nearly $5 billion grape, grape juice and wine industry, and also stands as the country’s second-largest apple producing state. In Pennsylvania, spotted lanternflies have damaged at least a half-dozen vineyards from 2017 to 2018. While there are no reports of spotted lanternfly infecting apple orchards in the U.S., the insects have damaged apples in Korea.
In late 2017 Clifton and Hajek began responding to reports of fungi killing the insects in Berks County, Pennsylvania. In early October 2018, they investigated a site near an apple orchard. “It was clear anywhere you walked, you’d see dozens of lanternflies killed by Beauveria on the ground, and then you’d see cadavers all over the trees killed by Batkoa,” Clifton said. At the same time, they have just one ant, one stonefly, and a beetle killed by Beauveria and no other insects killed by Batkoa in the area.
Back at the lab, the researchers used genetic techniques to identify the two fungi. They found that 97% of lanternflies on tree trunks were killed by B. major, while on the ground 51% of cadavers were killed by B. bassiana and the rest by B. major.
Very little is known about B. major. “This fungus is more difficult to grow in the lab than Beauveria bassiana,” Clifton said. In nature, insects pick up spores of B. major on contact, and the fungus then enters the insect’s body through weak spots in the outer cuticle or “skin”. This fungus tends to anchor its dead insect host to a plant or tree as the spores start to develop on the outer body and the infective spores are then shot off. Spores are produced for a short period of time, and after spores have spread and infected new lanternflies, traces of them in the environment are hard to find. Hajek intends to study B. major further in the future.
B. bassiana, a soil fungus, has been heavily researched. It belongs to an entirely different order of fungi from B. major, though the two infect insects in a similar manner, through surface contact, and both kill insect hosts.
The success of invasive species has been partly attributed to a lack of natural enemies. Conversely, Clifton suspects that one reason these two fungi infect spotted lanternflies but not other local insects is that the lanternflies lack the immunity that has evolved in local species, though more research is needed to verify the theory.
Clifton and Hajek plan to search the area for other insects known to be susceptible to these fungi, collect soil samples from the area, quantify the density of these fungi and test biopesticides based on B. bassiana. Some have already been approved by the Environmental Protection Agency.
“If you like apples, if you like grapes and wine, if you like beer (which requires hops, another plant eaten by spotted lanternflies), spotted lanternflies can attack those, and that has growers worried,” Clifton said.
Louela Castrillo, an entomologist at the United States Department of Agriculture (USDA) Agricultural Research Service on Cornell’s campus, and Andrii Gryganskyi, a molecular biologist at L.F. Lambert Spawn Co., are co-authors of the study.
The study was funded by the USDA.