Virginia Tech Works To Save Hemlocks

BLACKSBURG, Nov. 11, 2002 -- With the establishment of an insectary and the dedication of an entomology doctorate student, hemlock trees along the Eastern United States may have another way to fight their battle against the hemlock wooly adelgid.

The adelgid, a small aphid-like insect, feeds on the needles of the hemlock, eventually leading to the death of the tree. Ph.D. student Ashley Lamb, however, is spending her time researching another tiny predatory insect that might counteract the adelgid's lethal effect on trees.

The predatory beetle being raised in the insectarium to fight the adelgid's is the Laricobius nigrinus, a type of toothneck fungus beetle from the Pacific Northwest. They are capable of eating approximately 1,000 adelgid's during their lifetime, and they attack the insect in two stages: as adults and eggs. While there are many programs running along the East Coast to help solve the problem, Lamb feels the Laricobius is one of the better prospects.

"This is the only predatory beetle being researched which can work with other beetles," said Lamb. "It's the only one that is winter-active, which gives it the ability to disappear when the other beetles reappear, causing no interaction or interference. This is very critical, because the only way to succeed is through multiple agents."

The hemlock is not an economic tree, and therefore many people do not understand how important it is to the ecosystem, Lamb explained. Its loss would present real environmental repercussions. It is relied upon by many species of animals and insects, and it is a very unique tree to the ecosystem, and therefore cannot be replaced. Many fear that if the tree disappears, the species that rely upon it will be soon to follow.

Time, therefore, has continued to be a major issue with the project. The adelgid's infestation has spread down to South Carolina, up to Vermont, and west into the Smokies. There have even been a few scattered reports from Ohio. From the time of infestation, some trees last up to ten years, while most die out in around three to four years. That, Lamb said, is an extremely fast decline for a tree.

Another area in which time has played a factor is in the rearing of the laricobius in order to act as an effective predator.

While Lamb and other researchers were hoping to put the beetles into the field this year, the goal no longer seems realistic due to rearing constraints. Despite extensive research, there has been a high mortality rate during the late summers. Lamb commented that this arises due to an early emergence from summer dispause. The beetles are coming out of their summer hibernation too early, and they therefore starve due to the adelgid's also being in their hibernation stage.

"In order for the program to have any real chance of success," says Lamb, "we have to figure out the cues to regulate time. Our lab and field results have been successful with those beetles that survive the winter and summer in Virginia, so if we can find out how to keep them alive in the lab, the program may stand a real chance of succeeding."