Native fungi may offer safe, natural, biological control treatment for invasive sap-feeding insect
The season of daylight and blooming flowers has finally arrived. But, along with the emergence of all things green, comes the emergence of all sorts of flies, bugs, mites, worms, and mollusks. Many of these are unwelcome home, garden, and agricultural pests which, as the weather continues to warm, will only become more active.
Early season leaf- and plant-feeding insects are on every grower’s mind. And this year, grape growers, orchardists, nursery operators, home-gardeners, and others are advised to be aware of the potential for the appearance of yet another invasive pest from Asia.
Lycorma delicatula, the spotted lanternfly, is an invasive, sap-feeding plant-hopper, first discovered in the United States in Berks County, Pennsylvania in 2014. Although field observations indicate that tree of heaven, (Ailanthus altissima — itself an introduced invasive species that occurs throughout much of the U.S.) and grapevine (Vitis vinifera) are the insects’ preferred hosts, SLF is known to feed on a wide range of plants including, but not limited to, blueberries, hops, apples, plums, cherries, peaches, nectarines, apricots, almonds, oak, walnut, poplar, willow, and pine. The insect will often change hosts as it goes through its developmental stages.
Well-established populations now exist in and around Berks County, where feeding, by sometimes thousands of SLF, stresses plants, making them vulnerable to disease and attacks from other insects. Lanternflies also excrete large amounts of sticky ‘honeydew,’ which attracts sooty molds that interfere with plant photosynthesis, stunting growth and causing decline and, in extreme cases, death.
A quarantine regulating the movement of plants, plant-based materials, and outdoor household items now encompasses Berks and thirteen other contiguous Pennsylvania counties, as well as three counties in New Jersey, one in Delaware, one in Maryland, and one in Virginia; an area of more than 3,000 square miles.
Although no well-established populations have been identified anywhere in New York state, SLF has been confirmed in Suffolk, Westchester, Delaware, Albany, Chemung, Yates, and Monroe counties. All but one of the insects was dead when discovered.
SLF has been similarly confirmed in Connecticut and Massachusetts, as well as in locations in Pennsylvania, New Jersey, and Delaware outside of the quarantine area. It has not been reported in northern New York.
While lanternflies can jump and fly short distances, they are dispersed primarily through human activity. This is because, unlike most insects which lay their eggs on a living host-plant or in the soil in which the host-plant grows, SLF commonly lay their eggs on non-host, often man-made materials and structures, including brick, stone, firewood, lumber, outdoor furniture, trash barrels and, more importantly, cars, trucks, railcars, and shipping containers.
If allowed to spread, SLF has the capacity to seriously harm viticulture, orchard, logging, nursery, and tourism industries. At this time, the full extent of economic damage the insect could cause is unknown, but Pennsylvania’s grape, tree-fruit, hardwood, and nursery industries generate agricultural crops and forest products worth nearly $18 billion annually. New York’s grape juice and wine industries alone generate nearly $5 billion a year. New York is also the nation’s second-largest apple producer.
Scientists and researchers still have much to learn about SLF. Their host range remains poorly understood. And, other than tree banding, there are no established methods for detecting the spread of lanternfly populations and no phenology models to predict development.
Invasive insect species are often successful because, in their new environment, they have high reproductive rates and few, if any, natural enemies (predators, competitors, parasites, diseases). But researchers looking to contain and control SLF have reason to be hopeful.
A paper titled “A pair of native fungal pathogens drives decline of a new invasive herbivore,” published last month in the Proceedings of the National Academy of Sciences, reports that two naturally-occurring but unrelated fungi, Batkoa major and Beauveria bassiana, have been parasitizing SLF populations in Berks County, Pennsylvania. Researchers there confirmed that SLF found dead on the ground were killed by both B. bassiana (49%) and B. major (51%). Almost all (97%) of those found dead on trees were killed by B. major. The fungi appear to have only minimal impact on native insect species.
Eric Clifton, a Cornell University postdoctoral researcher and co-author of the paper, describes these findings as “a great example of how a major new invasive herbivore can be suppressed by native pathogens.” adding that “Nobody stepped in to do this; it all happened naturally.” He hypothesizes that native insects may have built up a resistance to the fungi over time, but SLF, because they may have never encountered these native fungi before, are unusually vulnerable.
Still, according to Clifton, “This is no guarantee that” these fungi are “going to stop the spread of lanternflies.” He’s says. It’s not going to kill all of them. But there is a chance that it will at least help to stabilize populations into the future.”
The paper, in its entirety, can be read online at pnas.org/content/pnas/116/19/9178.full.pdf.