In late November through early December, as most plants and insects head into a period of dormancy, the aptly named winter moth (Operophtera brumata) awakens from the soil. Native to Northern and Central Europe, they have been accidentally introduced several times to eastern North America since the 1930’s, where their larvae have been found defoliating our deciduous trees, preferentially oaks, maples and cherries. In this narrow winter window, male moths fly in search of a mate as the flightless females crawl up the bases of trees, exuding a pheromone to lure in the males. By using those pheromones to our advantage, LIISMA is helping researchers track the moth and gathering data for future work in biological control.
Researchers in the Elkinton Laboratory at the University of Massachusetts, Amherst have been capitalizing on this late season courtship ritual for nearly two decades. Jeremy Andersen, a post doctoral researcher in the Elkinton Lab, studies the biology and spread of the winter moth in the Northeast. His work is part of a project to establish sustainable biological control agents, such as the tachinid flies that have been successful in Canada, to control the moth populations. The LIISMA team, along with our partners at CCE Suffolk, have one small part in this: we’re assisting Andersen by deploying a handful of insect traps from Hempstead to Montauk. While the outside of the traps resemble a green milk carton, the real magic is inside– a chemical formulation of the female winter moth pheromone that will attract the love-struck and doomed male moths.
All this is done to reduce the damage generated by the moth’s larvae that emerge from their reddish-orange egg mass in early March. As the temperature nears 55ºF, the chartreuse inch worms drop down on silk threads and ‘balloon’ through the air to nearby trees and shrubs. Aside from important forest trees, they also feed on crops like blueberries, apples and cranberries. Upon landing, they burrow into unopened leaf and flower buds and commence feeding. Once the bud has been sufficiently consumed, they will migrate to a new bud and repeat the process; continuing to feed on the leaves as they unfurl. Their hatch timing in the early spring is crucial to the strategy of winter moth larvae as these young leaves are both easier to eat and more nutritious; young leaves have lower levels of plant defense compounds, like tannins, that would otherwise deter their herbivory. And instead, young leaves are high in nitrogen, which is a great source of protein for insects. Heavily infested trees can become completely defoliated, which can lead to stress and decreased growth, with potential to kill branches or entire trees.
To make things a little more difficult, there is a native look-alike to the invasive winter moth: the bruce spanworm (O. bruceata). Bruce spanworms are attracted to the winter moth pheromone, causing them to also fall prey to the traps. In sites where winter moth may just be getting established, traps may collectively contain a few hundred bruce span worms, and just a handful of individual winter moths. Extracting DNA from each individual moth can be costly, and while the Elkinton Lab has devised a method to tell the species apart using moth genitalia morphology, this can be a time consuming and task; as moths get damaged or begin to break down before identification can take place. These methods of moth ID also further delays the time a management response is made in emerging sites. Which is why it is so exciting that this past year the Elkinton Lab received funding from the USDA Forest Service to begin developing novel methods to monitor the spread of winter moth, including the use of environmental DNA (eDNA). eDNA refers to the small traces of DNA that can be found in soil, water, the air; and in this case, on the interior surface of the traps used to catch winter moths. By testing these various environmental samples, researchers can better understand the distribution of all kinds of species by measuring the relative quantity of DNA, without having to see the actual amount of a given organism like plants, animals and insects; natives and emerging invasives alike. In this way, the lab can then take samples from the traps themselves, and more quickly see which ones have winter moth DNA, allowing them to “triage” those sites where winter moth DNA has been newly detected. As well, they can get estimates of the abundance of winter moth in proportion to Bruce spanworm, and roughly evaluate how bad the infestations at each location are. Andersen goes on to say, “These results will be used to determine how fast winter moths are spreading, and high-density locations will be targeted for potential biological control releases.”
As previously mentioned, biological controls have already been a success for controlling the winter moth in Canada, using the tachinid flies Cyzenis albicans and Agrypon flaveolatum. As oak and apple leaves become defoliated by winter moths, the leaves produce a volatile compound which attracts the biocontrol agent flies, who then lay their eggs along the remaining leaf edges. When the winter moths feed, the fly larvae get consumed and take up residence in the moth’s salivary glands. As moth larvae drop to the ground to pupate, the fly larvae stay inside of the moths, completing their life cycle within and ultimately killing the moth, thus preventing them from emerging as adults. While these flies may not completely eradicate the winter moth, they are one more adaptive management tool that can help reduce the impact that this invasive insect might have on our native trees.
(Check out this UMass Amherst Extension article for more detailed recommendations for managing winter moth on your property).
As we begin collecting our green winter moth traps and sending them back to Andersen in Massachusetts, we look forward to the results of his work and that of his colleagues in the Elkinton Lab!
