Spotted lanternflies, the invasive planthoppers known for their destructive impact on agriculture, may possess a built-in chemical defense that renders them foul-tasting to native bird predators. According to new research, the insect’s choice of food plays a crucial role in its palatability, with individuals that feed on the invasive tree of heaven becoming particularly unappetizing. This dietary habit allows them to store, or sequester, toxic compounds from the plant, creating a protective shield that helps them thrive in their new environments.
This finding suggests a complex ecological interaction where one invasive species helps another fend off local predators. Researchers from Penn State’s College of Agricultural Sciences discovered that birds show a clear preference for lanternflies that have not fed on the tree of heaven, indicating they can detect the acquired toxins. The study clarifies why the brightly colored insects have faced limited pressure from birds, a factor that has likely contributed to their rapid spread across the eastern United States since their arrival in Pennsylvania in 2014. Understanding this defense mechanism is a critical step for scientists developing broader strategies to manage the economically damaging pest.
An Invasive Partnership
The key to the lanternfly’s defense lies in its relationship with its preferred host, the tree of heaven (Ailanthus altissima). Like the lanternfly, this tree is an invasive species that originated in the same region of Asia. The plant is known for producing potent defensive chemicals, including a class of compounds called quassinoids, which are notoriously bitter and can be toxic. Researchers hypothesized that when spotted lanternflies feed on the sap of the tree of heaven, they ingest and accumulate these chemicals in their own bodies, a process known as toxin sequestration. This adaptation is not unique in the insect world, as famously demonstrated by monarch butterflies, which become toxic to predators by feeding on milkweed.
The bright coloration of adult lanternflies may serve as a warning to predators. Their red and black hindwings exhibit a classic aposematic signal, a visual cue that advertises unpalatability or toxicity. This “warning coloration” tells potential predators that the insect is not a worthwhile meal, discouraging attacks. The research suggests that birds learn to associate the vibrant display with a negative experience, such as a bitter taste, leading them to avoid the insects in the future. This learned avoidance would give the lanternflies that have fed on tree of heaven a significant survival advantage.
Testing Predator Preferences
An Experimental Cafeteria for Birds
To determine if birds were actually deterred by lanternflies that consumed tree of heaven, entomologists conducted a series of controlled experiments. The research team, led by postdoctoral researcher Anne Johnson under the guidance of professor Kelli Hoover, reared colonies of spotted lanternflies in controlled environments. One group of lanternflies was raised on a diet that included tree of heaven, while the other group was fed alternative host plants that do not contain the same toxins. This allowed the scientists to isolate the effect of the diet on the insects’ appeal to predators.
The team then presented both types of lanternflies to a variety of wild birds, including nesting house wrens, to observe their feeding choices. The results were consistent: the birds significantly preferred to eat the lanternflies that had not fed on the tree of heaven. This preference strongly suggests that the insects that consume the invasive plant acquire chemical defenses that are detectable and repellent to avian predators. While the specific quassinoids are known to be bitter to mammals, this study provides the first direct evidence that they also create a foul taste for birds.
A Chemical Shield at Work
The defensive compounds at the center of this interaction are quassinoids, a group of naturally occurring chemicals found in the tree of heaven. These substances are known for their intensely bitter taste and have various toxic effects. By feeding on the tree, the spotted lanternfly effectively arms itself with these chemicals, turning its own body into a distasteful and potentially harmful meal for a predator. This strategy helps explain the pest’s remarkable success in establishing itself in new ecosystems where it has few natural enemies.
The presence of this chemical defense complicates efforts to control the lanternfly population. While birds are often seen as a natural, eco-friendly solution to insect pests, their effectiveness against the spotted lanternfly appears to be limited by this dietary factor. If the most abundant host plant makes the lanternflies inedible, then birds will not be able to exert significant predatory pressure to keep the population in check. The research underscores that the lanternfly’s invasiveness is not just a matter of its own biology, but is deeply connected to the presence of another invasive species, the tree of heaven.
Implications for Pest Management
These findings have significant implications for how state agencies and property owners combat the spotted lanternfly. The study suggests that managing the tree of heaven could be a crucial component of an integrated pest management strategy. By removing the invasive tree, it may be possible to make local lanternfly populations more vulnerable to predation by native birds. If the insects are forced to feed on other plants, they would not acquire the same level of chemical defense, making them a more appealing food source for birds like catbirds, woodpeckers, and wrens.
However, complete eradication of the tree of heaven is likely impossible due to its widespread and prolific nature. Scientists advise that removal efforts on a local scale, such as in residential neighborhoods, farms, or vineyards, could still be beneficial. Creating a landscape that is less favorable to the lanternfly’s defensive strategy, while simultaneously encouraging the presence of native birds through feeders, bird baths, and appropriate habitat, could help foster a more effective natural control system. Ultimately, controlling this invasive pest will require a multi-pronged approach that includes public participation, targeted removal of its preferred host, and leveraging natural predator-prey dynamics wherever possible.