Should the world end in ice, the cockroaches will have some company.
The frigid temperatures in Pennsylvania during the latter part of this winter have contributed to a die-off for at least one species, but it hasn't been enough to faze some of the others with the potential to damage forests.
"It depends on which bug you're talking about," Donald Eggen, forest health manager with the Pennsylvania Department of Conservation and Natural Resources (DCNR) noted.
Gypsy moth caterpillar
DCNR issued a statement Friday citing the impact below-average temperatures have had on the Hemlock Woolly Adelgid. According to the report, the agency is seeing massive die-offs of the invasive species.
"Right now, the insects are starting to become active, so it doesn't have to get that cold to impact them," Eggen said. "We're pretty much finding 100 percent die-offs."
The release supported Eggen's statements. According to it, the state bureau of forestry has collected hemlock branch samples from more than 75 sites and found wide-spread die-off.
The release specifically cited samples from Cook Forest State Park, in which only one of 308 adelgids counted was found to be alive.
Statewide die-off observations were not as high as in Cook Forest, but still accounted for a significant portion of population, according to the release.
"Caution is the watchword here as our entomologists point out remaining insects can foster infestation in a short time, even to areas where there was 100 percent die-off this winter," DCNR Secretary Ellen Ferretti said. "To be sure, the widespread insect mortality presents time for the health of hemlocks to improve through new growth. Time for land managers along the leading edge of the infestation to get their plans developed and implemented to combat the infestation."
"It gives us time to catch our breath," Eggen said, adding, "[Adelgids] can suffer up to like 90-some percent reduction and still re-populate."
Eggen noted this is possible because all Hemlock Woolly Adelgids are female and lay eggs, so even a single specimen can re-populate an area.
"Insect and diseases that infest trees are always of concern to us, and the prolonged cold this winter has caused mortality of hemlock woolly adelgid that was sampled from the Allegheny National Forest and other lands the area," Andrea Hille, forest silviculturalist for the Allegheny National Forest, said. "I cannot speak for the other insects that may have been impacted by cold temperatures. Unfortunately, the 5 percent or so of hemlock woolly adelgid that did survive the winter is the cold hardy segment of the population, and these are the adelgids that will lay eggs and produce young that may also be more cold hardy."
He also pointed out the species has a biannual generational cycle, meaning they reproduce twice per-year. The die-off only impacts the over-winter cycle of reproduction.
The Hemlock Woolly Adelgid was first detected in the state 45 years ago, in 1969, and has been spreading ever since. It has only spread to the Allegheny Plateau region recently, in large part because of cooler temperatures, but had already been found in the rest of the state.
"You get further south to the Smokies (mountains), where it never gets real cold and the hemlock are devastated," Eggen said.
The species, which originated in Asia, feeds on the fluids within Hemlock branches. While the species has come to threaten the entire Eastern United States, it is particularly worrisome in Pennsylvania, where it feeds on the state tree, the Eastern Hemlock.
Other potentially-damaging species, however, won't be impacted as heavily by the cold. Eggen assessed the potential impact of the weather on two other species, the Emerald Ash Borer and Gypsy Moths.
"In my opinion, the larvae over-winter under the tree bark," he said of the ash borer. "There is some die-off from thinner bark trees, but a really thick bark, it acts as insulation. It cuts back come, but are you going to eliminate it? I don't think so."
As for gypsy moths, the species which is his area of concentration, Eggen said the moths lay egg masses at ground level, which allows snow to act as insulation.
"In my entire career, I've seen that one time," he said of conditions severe enough to cause a large die-off. "So the gypsy moths are going to be just fine."