Insects wage war on hemlocks – and each other
European settlers who ventured into the southern Appalachians found 500-year-old hemlocks with trunks 5 feet in diameter. Those graceful trees are mostly gone, logged for lumber and for bark used by tanneries.
The smaller, fewer hemlocks that remain are more important to forest life than to people.
Hemlocks thrive in shade and grow slowly, taking centuries to tower over other trees. Their dense canopies create cool, dark places that shade trout streams and sun-shunning herbs and shrubs. Nearly 90 bird species nest or forage among hemlocks.
Adelgid infestations of Eastern and Carolina hemlocks began after the insect reached Richmond, Va., in 1951 among a shipment of weeping hemlocks from Japan. Initially concentrated in the hemlock forests of the Northeast, the insects gradually moved south down the Appalachians.
The adelgid feeds on the sap at the base of hemlock needles, blocking the flow of nutrients. Needles begin falling off. Unable to harvest the sun’s energy, the tree starves to death within a few years.
Lari’s genius lies in the perfect timing of its attacks. One vampire bug feeds on another.
The beetle tracks adelgids by the scent of their sweet secretions, called honeydew. They attack in winter, when the hemlocks reach for the energy of winter sunlight and adelgids suck the trees’ sap.
The beetles “slit their throats and drink their blood,” entomologist Richard McDonald said, then lay eggs inside the adelgids’ cottony egg sacs. When the young beetles emerge, they wolf down adelgid eggs and nymphs.
Over its yearlong life, one beetle and its offspring can kill more than 70,000 adelgids.
This story was originally published March 29, 2015 at 2:00 AM with the headline "Insects wage war on hemlocks – and each other."