Photographer: ©entomart Source: Wikimedia Commons Copyright: CC BY 3.0 US
Adults: These butterflies are sexually dimorphic, meaning the males and females look different from one another. A winged male is pictured above. Females have the same coloration but they have stumpy wings, making them basically flightless. Their colors are inconspicuous and dull, allowing them to blend in with may tree’s bark patterns.
Larvae: The caterpillars are light green with a white longitudinal strip running down both sides of the body.
Winter moths are defoliating moths, stripping trees of their leaves at distressing rates. In heavily infested trees the larvae also attack leaf buds from within, causing bud death. Up to 150,000 leaf defoliating caterpillars can be present on the average infested tree. In cases where they attack fruit trees, harvests are severely reduced. Studies have shown that defoliation by winter moths can reduce annual radial growths of Oak and Maple species by 67%. Defoliation can significantly stress a tree, and even kill it within a few years.
Operophtera brumata is called the winter moth because adults emerge from the soil around Thanksgiving and throughout December. Males fly around while females climb up the trunk of the trees. Females attract winged males by sex pheromones. After mating, females lay 100-200 eggs in clusters under bark scales on tree trunks, and then die. The eggs hatch into caterpillars in the spring. The larvae feel upon the leaves of the tree, and within leaf buds. Once feeding ends in mid-June the caterpillars migrate to the soil for pupation.
Introduced from Europe to Nova Scotia in the 1950s. In the 1990s it was found to be the main cause of Oak and Maple dieback in Massachusetts. It has since established in some New England states, and in the Pacific Northwest.
Europe and Western Asia
U.S. Habitat: Given their winter-cycle, this moth may be intolerant of areas with mild winters.
U.S. Present: CT, MA, ME, NH, OR, RI and WA
The male of the native Fall Cankerworm (Alsophila pometaria) is similar to winter moth males, but has a distinctive light colored patch near the distal end of the front wing on the leading edge.
Studies have shown that the winter moth is able to reproduce with the closely related and native defoliating moth, Operophtera bruceata. This may be allowing it to spread its distribution farther than it would without hybridization.
Researchers in Nova Scotia have been studying this pest for decades, working on best management practices and successful survey strategies. The adults cannot be successfully managed. Luckily, the eggs and larvae are quite responsive to several physical, chemical and biological controls. For the eggs, one can apply an oil spray that suffocates the eggs, preventing them from developing. Newly hatched caterpillars are very susceptible to Bacillus thuringiensis (Bt) which is a commonly used control method for several pests. However, on older caterpillars Bt is not as effective, but Spinosad, Sevin, and Neem Oil seem to work quite well.
Elkinton, J. S., Boettner, G. H., Sremac, M., Gwiazdowski, R., Hunkins, R. R., Callahan, J., ... & Campbell, N. K. 2010. Survey for winter moth (Lepidoptera: Geometridae) in northeastern North America with pheromone-baited traps and hybridization with the native Bruce spanworm (Lepidoptera: Geometridae). Annals of the Entomological Society of America, 103(2): 135-145.
Elkinton, J. S., Liebhold, A., Boettner, G. H., & Sremac, M. 2014. Invasion spread of Operophtera brumata in northeastern United States and hybridization with O. bruceata. Biological Invasions, 16(11): 2263-2272.
Simmons, M. J., Lee, T. D., Ducey, M. J., Elkinton, J. S., Boettner, G. H., & Dodds, K. J. 2014. Effects of invasive winter moth defoliation on tree radial growth in eastern Massachusetts, USA. Insects, 5(2): 301-318.