Latin Name: Melanophila fulvoguttata (Harr.)
Common Names: Hemlock Borer, Flatheaded Borer
The hemlock borer is a native insect found from Newfoundland to Alberta. It is considered a secondary attacker - an insect that usually arrives after some other agent has severely weakened or killed the tree i.e. storm damage, windthrow, drought, stand opening, insect attack. It has been observed attacking live, mature, eastern hemlock trees in western Nova Scotia.
This "flatheaded borer" is known to attack balsam fir, tamarack, red, white and black spruce, eastern white pine, and eastern hemlock.
There have been no recorded outbreaks in Nova Scotia. In areas where outbreaks do occur, they happen in ten year cycles lasting 3 - 5 years.
Dead trees attributed to hemlock borer attacks have been observed in western Nova Scotia. Extreme climatic conditions similar to those described below have occurred and are expected to continue or accelerate with climate change. This, coupled with a Pale Winged Grey outbreak in that area, adds to the already high level of stress in the eastern hemlock forest.
From: Climate Variability and Change in the Great Lakes Watershed
" . . . the late 1930s, the hemlock borer, ordinarily not a problem, reached epidemic proportions. Careful examination (Secrest et al., 1941) revealed that extensive root damage had occurred during the drought years 1930-1937. Borer attacks in 1938 were successful only on trees that had 10 % or less of their root system still alive. In 1939, attacks were successful only on trees with less than half of the main lateral roots alive. Obviously, hemlock borer attacks were successful only on trees that were already heavily damaged by unfavourable climatic conditions.
The 1930s droughts were ultimately responsible for the loss of trees near the range limit, but insect attack was the proximate cause of death of trees already weakened by drought. The insight to be gained from this example is that unfavourable climatic conditions may not kill trees outright, but by stressing the trees, climate can contribute to death by insect attack . . ."
The hemlock borer has a 1 or 2 year life cycle, depending on what time of year Larvae and galleries under bark the eggs are laid. Those laid in late summer will overwinter two years; those laid in early summer just one winter.
Eggs laid in early summer: the tiny, oval, white eggs are laid in groups in bark crevices of weakened or dead trees and logs. Approximately two weeks later the larva hatches and bores into the moist cambium layer and begins to feed, forming a feeding gallery. By late fall, the 2.5 cm long larva ( Photo Credits: Ron Kelley, Vermont Dept. of Forests, Parks and Recreation ) constructs a pupal chamber in the outer bark, where it overwinters as a pre-pupa. Pupation occurs the following spring, with the adult beetle ( Photo Credits: Ron Kelley, Vermont Dept. of Forests, Parks and Recreation ) emerging from June until August.
Eggs laid in late summer: the tiny, oval, white eggs are laid in groups in bark crevices of weakened or dead trees and logs. Approximately two weeks later the larva hatches and bores into the moist cambium layer and begins to feed, forming a feeding gallery.
The larva overwinters in the cambium, then continues to feed and develop during the following summer. In the fall, the larva constructs a pupal chamber in the outer bark, where it overwinters as a pre-pupa. Pupation occurs the following spring, with the adult beetles ( Photo Credits: Ron Kelley, Vermont Dept. of Forests, Parks and Recreation ) emerging from June until August.
Cutting, removing, and processing infested trees quickly can prevent population buildup. If selective cutting is undertaken, it is important to keep heavy equipment use to a minimum in the stand to reduce damage to these shallow rooted trees. If this is not practical, on site destruction (burning), or removing the bark will kill the larvae. This will also make the tree unsuitable to support further brood production.
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