Winter Moth

January 03, 2024

Yesterday’s local newspaper carried a USA Today article on how the state of Rhode Island is dealing with unwanted visitors.  An invasive moth from Europe is causing widespread damage to hardwood trees and blueberry (section Cyanococcus within the genus Vaccinium) crops.  According to Alana Russell with the Department of Environments Management (DEM), infestations in Rhode Island were knocked down in coastal communities by introduction of a parasitic fly (Cyzenis albicans) that feeds solely on the moths and is not seen as a threat to other insects or vegetation.  Between 2011 and 2017 scientists from the University of Rhode Island and the DEM released 2000 flies into eight Rhode Island communities.  Testing for the presence of the winter moth is done by placing traps in trees with the pheromone of the female moth in order to attract and trap the males.

When I looked online, I found the winter moth (Operophtera brumata) is a moth of the family Geometridae.  The moth is an abundant species in Europe and the Near East and is a famous study organism for evaluating insect population dynamics.  It is one of the few lepidopterans (moths and butterflies) of temperate regions in which adults are active in late autumn and early winter.  The adults use internally generated heat (endothermy) for movement in cold temperatures.  The forewing color of the winged males varies from greyish yellow to beige-brown or a slightly reddish-tint.  The patterns are often band-shaped dark brownish, with a yellowish fringe.  The hindwings are pale grey or yellow grey.  The antennae are short and finely hairy.  The female winter moth has greatly reduced wings and are flightless.  Body length for adults of both sexes is around 0.4 inches (1 cm).  The larvae are 0.1 inches (2.5 mm) in length after hatching and grow to 0.75 inches (19 mm) over a six-week period.  After the first frost in late fall the females emerge from their pupae and move up the trees where they emit pheromones in the evening to attract males.  After fertilization, they move higher to lay an average of 100 eggs each.  The larger the female moth is the more eggs laid.  In North America, the winter moth can be confused with a related native species, the Bruce spanworm (Operophtera bruceata), and the two species have hybridized.

The winter moth is native to Northern and Central Europe and genetic populations in Europe are a result of recolonization following the last glacial period (12,000 BP).  The winter moth is considered an invasive species in North America with the first confirmed infestations in Nova Scotia, Canada, in the 1930’s.  It was later accidentally introduced to Oregon (1950’s) and Vancouver Island, British Columbia around 1970.  Defoliation by the moth was first noted in the US in eastern seaboard states in the late 1990’s.  The moth is now well established in Massachusetts, Rhode Island, Maine, and New Hampshire.  Expansion inland and north in New England appears to be curtailed by cold winter temperatures and the species is found along the coast but not far inland.  Milder winters from global climate change may be allowing local expansion of the moth’s territory.  A study conducted in Massachusetts documented that winter moth defoliation reduced the annual trunk diameter growth rate of oak trees by an average of 47% while not significantly impacting growth rates of the less defoliated maple trees.  Efforts at biological control are underway.

THOUGHTS:  The winter moth is believed to have arrived in North America from Europe along with infected nursery stock.  An article published in Molecular Ecology in 2021 suggested there were four successive invasions that account for the spread along the northern Atlantic and Pacific coasts of the continent.  That would imply negligence in shipping procedures throughout the 20th century.  What is the adage, “fool me once . . .”  Act for all.  Change is coming and it starts with you.