They’ve gone quiet now, but are out there still, and the questions remain. Why call them gypsy? Should we change to Roma*? Or use their Latin name: Lymantria dispar? That last word certainly describes the feeling evoked when seeing our favorite trees in tatters. But why this year? (When I was feeling so smug about our cicada dodge.) How long will the outbreak last? And will they be here in the same numbers next year? I went in search of answers.
In an unChronicle move, I first opted to dig into the Web of Science, a database repository of science articles, to see what folks who study dispar full time say. A recent study (Zubrik et al., 2021) summarizes data stretching between 1945 and 2020. While some information was region specific, given the “everywhere” nature of the beast, many insights likely hold for Cornwall. For instance, the airborne larvae can travel with wind up to 15 kilometers. Good lord, are they bumping into Covid-19 hurtling around out there?
If we think of their population dynamics over time, it appears that after a period of build-up, an “outbreak” threshold is reached every roughly 8 (but as many as 12 or as few as 6) years, the outbreak lasts on average 3 years (but between 1.5 and 4), then there is a population collapse (they’ve eaten all the available food or some genetic failing strikes) and the population build-up phase begins again. The species is polyphagous meaning they are happy to eat almost any foliage, chomping on about 85 different trees in the US, though preferring deciduous to conifers.
A knowledgeable source closer to home is Thomas Worthley, Associate Extension Professor at UConn, who responded to Ella Clark’s inquiry for advice. “Except in rare circumstances, such as what occurred in Eastern CT in 2016 and 2017, defoliation by gypsy moth caterpillars is a temporary and cyclical event. Population outbreaks occur periodically, when factors in the environment that generally keep the population stable are not quite in balance. Usually, healthy oaks and other hardwood trees can withstand an episode of defoliation, they will set new buds and produce a new set of leaves to finish out the growing season. The effect shows up as smaller than normal growth rings. Softwood trees such as pines and hemlocks can be killed, however, with a single defoliation. Repeated defoliation events in subsequent years can be problematic because the carbohydrate reserves that trees need for refoliation can become exhausted. Also, if there are additional stress factors involved such as drought or other pests tree mortality can occur. There is not much an individual can do except wait for the infestation to run its course and make sure individual trees get plenty of water.” This last comment because the caterpillars compensate for poor foliage in drought conditions by eating more leaves and causing more defoliation. Worthley recommends the CT Agricultural Experiment Station web pages for more information.
Long-time gardener Roxanna Laughlin recalled a past similarly intense outbreak, when she chose to spray her favorite orchard trees but let the rest hang on as best they might. Ants, stinkbugs and small mammals all feed on different stages of the moth’s life cycle providing a reason, finally, not to hate the white footed mice.
*In early July, the Entomological Society of America announced it was removing “gypsy moth” as a recognized common name for the insect.
📷: Jonathan Landman (featured, 1, and 3); Lazlo Gyorsok (2, 4)