Male Winter moth fits inside circle the size of a nickel. Females are just under a half-inch in length. |
An insect invasion has plagued eastern
The "winter" part of the name refers to an evolutionary
strategy used to avoid predation. Most insect eaters (birds, bats, spiders, wasps
and other insects) are active during warmer months. Winter moths shift the
active parts of their life cycle into the colder months. Eggs are laid in late November and December and hatch in late March. The tiny hatchlings eat the beginning-to-open
flower and leaf buds from the inside out.
Female, note small wings |
Winter moths have an interesting dimorphism. Males have
strong flight muscles, with an ability to pre-warm these muscles through
shivering before cold weather flight. In contrast, females have only vestigial
wings. Sacrificing flight capacity allows more than fifty percent of their adult
body weight to be given over to eggs. Mating is achieved after the females
climb up tree trunks and then release scent pheromones into the air. Males fly
to them.
Winter moth larvae are generalists, but especially like
fruit trees, maple, ash and birch trees, and blueberry bushes. Flower bud
damage leads to low fruit and berry yield. Leaf loss can be so great that too
many years in a row will kill trees, especially if dry conditions prevail
during the time the trees are putting out replacement leaves. Treatment
involves putting sticky products such as Tree Tanglefoot around tree trunks in
November and then spraying a few times in early spring with dormant oil or other insecticides. There are organic
treatments for those who do not want to use chemical pesticides.
11/14/14 update: After a few night frosts, moths are beginning to appear in Maynard.
11/26/14 update: My big birch tree has more than 500 males and females stuck in goo!
12/15/14 update: No new sightings, so removed plastic wrap.
11/14/14 update: After a few night frosts, moths are beginning to appear in Maynard.
11/26/14 update: My big birch tree has more than 500 males and females stuck in goo!
12/15/14 update: No new sightings, so removed plastic wrap.
TreeTanglefoot on birch tree. Applied on plastic wrap, not directly on tree. See photo below for results. |
Gypsy moths occupy a different portion of the calendar than
winter moths. Eggs laid in August hatch the following May. The rest of the life
cycle is compressed into a few months. Nearly 140 years later, this pest's
territory is still expanding westward and southward, although a number of introduced
biological controls, including parasitic insects, have blunted severity of the
outbreaks.
Moth menage a trois stuck in the goop. Males are attracted to pheromones released by females. Click on any photo to enlarge. |
These two moth species are examples of slow expansion because females are unable to fly. Egg laying occurs on or near the tree they grew up on. Dispersion is achieved be a few methods. Post-hatch caterpillars can release a silk strand from the abdomen, then unclasp from the twig and allow wind to blow them to a new location.
This means of travel is better known for young spiders, and called 'ballooning.' Older caterpillars can descend to the ground and explore, one tiny footstep at a time. Either way, the failure rate is high, but enough succeed that territory continues to enlarge, and areas that are sprayed with pesticides will re-infest over time.
2015, and my birch trees' infestation was even worse. This year I got the goop on the tree by mid-November. Trapped so many that I had to remove it and reapply fresh wrap and goop on Thanksgiving, and then again December 1st. Will see come spring how much this slaughter benefited the trees. Biological control has proved successful in Canada - not clear if this method has yet been introduced to U.S. There are two insect species (a fly and a wasp) that specialize in winter moths. Their larvae consume the winter moth caterpillars from the inside.
2016: Less severe, and more males than females. That suggests I am getting my own local females and males, but additionally attracting males from the neighborhood. If this repeats in 2017, suggests that it is not necessary to wrap every tree, as wrapping only some trees will remove males from the mating equation. However, this is a strategy that works if males mate only once.