Predatory Beetles Released on the Channels State Forest

Researchers from Virginia Tech released 1,000 Laricobius nigrinus beetles into a stand of eastern hemlocks on the Channels State Forest. The tiny black beetles are known predators of the hemlock woolly adelgid (HWA). Raised under controlled conditions at Virginia Tech, the beetles are part of an ongoing research project under the direction of Dr. Scott Salom. 

The hemlock woolly adelgid (HWA) is a non-native invasive pest that is devastating eastern hemlock trees.  Since its introduction from Asia in the last century, the HWA has advanced throughout the range of the eastern hemlock, leaving a swath of dead and weakened trees in its path.  With a plentiful food source and no predators to slow it down, HWA has spread unchecked for decades. Chemical treatments can control HWA on an individual tree by tree basis; chemical control of HWA on a large-scale forest landscape is not practical.

Prior to its introduction in the eastern U.S., HWA was identified on western hemlocks in the Pacific Northwest. Western hemlocks have survived the HWA invasion much better than their eastern counterparts. The presence of predatory insects in the Pacific Northwest may limit populations of HWA.  From this comparison, it is generally accepted that the only effective means of saving our eastern hemlocks will be biological control.

Not much bigger than the bug that it eats, Laricobius nigrinus is a native of the Pacific Northwest.  And while it will feed on other species of adelgid, studies show that it prefers HWA.  Also, L. nigrinus is active during the winter months, which coincides with peak HWA activity. 

The slow-growing, shade-tolerant hemlocks provide crucial protection against erosion.  Hemlocks shroud and protect most of the cold streams that tumble down our mountains and provide increasingly rare habitat for native brook trout and many other species.  Multiple hemlock stands stretch along the numerous streams of the Channels State Forest. Over the next several years, the research team from Virginia Tech will monitor the selected hemlock stand to determine if the beetles are surviving, reproducing and having an effect on the HWA populations.  The tiny bug with a big name may provide an opportunity to save an important species.

Zach Olinger, Matthews State Forest