Spongy moths (Lymantria dispar) are a non-native insect species that feed on the leaves of trees when they are in the caterpillar stage.
They were accidentally introduced into the United States in 1869 as a potential alternative organism to the silk moths in order to bolster the growing silk industry in the U.S. After their escape from the Massachusetts laboratory in which they were housed, they became established and spread across the country.
Lymantria dispar undergo a complete metamorphosis with one generation per year.
The egg stage overwinters, with larvae emerging in late April/early May around the same time as oak bud burst. The larvae will feed on tree leaves through May until mid June.
Next, they enter the pupal stage for a few weeks where they emerge into adults.
Adults mate shortly after emergence, and lay eggs in July and August, where the cycle starts over again.
Spongy moth egg masses can contain about 600-700 eggs and are usually deposited in sheltered locations such as tree trunks, limbs, and under rocks.
Outbreaks of spongy moth occur with varying degrees of periodicity. Their numbers fluctuate widely each year, where a season with severe damage can be followed by a season with very little.
Lymantria dispar cause major damage to trees and forests when they are in high numbers, causing thousands of acres in damage and defoliation.
With the help of Dr. Danielle Garneau and members of the NYS DEC (Naja Kraus and Anna Carr), I commenced this study in order to evaluate the spongy moth population of Clinton county and surrounding counties. This study served to grow my field experiences, further develop data analysis skills, and provide the NYS DEC with regional Lymantria dispar data beyond their previous surveyed areas.
The goal of this research was to determine if local sites were above the spongy moth management threshold densities of 250, 500, and 1000 average egg masses/acre.
EXPERIMENTAL DESIGN
I utilized NYS DEC’s Lymantria dispar egg mass sampling protocol. At each site, I established 4 randomly placed circular plots and identified tree species, tree size (dbh), bark texture, as well as egg mass abundance and condition.
- Moth egg masses on the lower portions of tree trunks were counted first, based on new or old masses, and measured using a ruler.
- The rest of the masses were then counted all together
- Tree species were identified and DBH was calculated using a DBH tape
- Tree bark was also scored using a scale chart
RESULTS
The vertically cracked bark (type 4) of the eastern white pine (Pinus strobus) and northern red oak (Quercus rubra) were the most commonly infested. In addition, the plated bark (type 6) of the red pine (Pinus resinosa) and red spruce (Picea rubens) were also commonly infested.
CONCLUSION
The data collected in this study will inform future regional forest management for Lymantria dispar (spongy moth). Knowing areas of higher defoliation risk can help landowners better manage their forest for pests. The NYS DEC Lymantria dispar webpage (https://www.dec.ny.gov/animals/83118.html) offers many different methods of moth removal.
It is important to recognize the Lymantria dispar (spongy moth) stage, as management actions are stage-specific.
- Egg masses can be scraped off the tree and destroyed
- Caterpillars can be treated with insecticides
- Pupas can be hand picked and destroyed
- Many life stages can be controlled naturally by predation from birds, parasites and rodents
ACKNOWLEDGEMENTS
I want to thank Naja Kraus and Anna Carr from the NYS DEC for giving their insights into this study and providing data previously collected in other surveys for comparison. I would also like to thank DEC biologist John O'Connor and NYS Park manager Charles Hacker for granting me permission to perform permitted research at the sites.