The Grinch That Spoils Christmas
Laurie Koelling, executive director of the Michigan Christmas
Tree Association, and entomologist Robert Haack check Scotch pine for pine
shoot beetles at a tree farm near East Lansing.
Richard Dysart wasn't out collecting firewood when he cut and stacked pine
logs last summer in the woods near Lodeve, France. An entomologist with the
Agricultural Research Service, Dysart piled the wood to lure beneficial insects
that may soon dine on destructive pine shoot beetles in the United States.
Pine shoot beetles, Tomicus piniperda, turned up in Ohio in 1992.
They have spread to Illinois, Indiana, Maryland, Michigan, New York,
Pennsylvania, and West Virginia.
In 1995, this six-legged spoiler threatened growers of pine Christmas trees
in about 150 U.S. counties. But much more is at stake: 145 million acres of
pine trees30 percent of the nation's commercial timberland.
Some scientists believe the dark-brown, one-fifth-inch-long beetle stowed
away on ships from Europe entering the Great Lakes via the St. Lawrence Seaway.
The insects may have infested bark on rough-cut pine timber used as cargo
crates or braces, says Dysart. He's based in Montpellier, France, at ARS'
European Biological Control Laboratory.
To begin his search for natural enemies of Tomicus, Dysart first
tapped the existing base of research knowledge. He relied strongly on studies
by Montpellier colleague Franck Herard. Soon, Dysart focused on the biology,
life cycle, and behavior of a predatory beetle, Thanasimus formicarius.
One adult Thanasimus can eat about three pine shoot beetles daily for 2
or 3 months.
About three-eighths-inch long, Thanasimus resembles an antif
the ant were wearing a cape colored with wavy bands of brick-red, black, and
white. Scooting along pine trunks and branches, this predator strikes quickly.
First it pins Tomicus, using mandibles and four front legs. Then,
balancing on the back two legs and abdomen, it amputates the prey's legs, snips
its body in two, and eats the insides.
Laurie Koelling of Okemos, Michigan, hasn't seen Thanasimus in
action. In fact, she's seen only a few pine shoot beetles at the Christmas tree
farm she and her husband operate. But even one Tomicus can be too many.
The pine shoot beetle, Tomicus piniperda, is a
destructive pest of pine trees in about 150 U.S. counties.
To slow this beetle's spread, USDA's Animal and Plant Health Inspection
Service (APHIS) operates a quarantine in infested counties. If an inspector
finds just one in a field at a tree farm or nursery, none of the field's pine
trees, boughs, or logs can be shipped to Tomicus-free
countiesunless, that is, these pine products meet requirements to ensure
no live beetles accompany them.
"Some growers have lost contracts," says Koelling. She is
executive director of the Michigan Christmas Tree Association. Christmas trees
form a vigorous, $80 million branch of Michigan's economy, with 4 million sold
Evidence of Tomicus' nibbling typically amounts to a few dead branch
tips. These can be snipped off a Yule tree in seconds, and the pest doesn't
threaten wood structures and furniture. So, why all the fuss?
Because, says Robert Haack of USDA's Forest Service, "in Europe and
China, Tomicus beetles sometimes kill pine trees stressed by fire,
drought, or defoliation. We haven't seen this in the United States. But the
potential exists." In East Lansing, Michigan, Haack heads the Forest
Insect Unit at the North Central Forest Experiment Station.
"Tomicus has attacked all of the dozen or so pine species we and
our cooperators have tested," he says. "We're still evaluating spruce
and other conifers, although fir, tamarack, and Douglas-fir don't seem to
appeal to this beetle."
In early spring, adult pine shoot beetles emerge from winter
hideawaysholes in bark near the base of a live pine. They search for pine
branches, trunks, or stumps that died or were cut since autumn.
The female carves an egg gallerya 3- to 5-inch tunnel, just beneath
the bark. A male Tomicus appears, they mate, and she lays 50 to 100
eggs. She may set up three or four galleries before dying.
Eggs hatch and develop into hungry larvae. They dine on tree phloemthe
inner bark, nonwoody vascular tissueadding dozens of chambers to the egg
gallery. Weeks later, young adult beetles depart the galleries. They spend
summer maturing sexuallyand tunneling in pine branch tips.
On tree farms, Haack says, growers may use IPM (integrated pest management)
techniques to deprive Tomicus of breeding sites. Forest Service
researchers and colleagues with APHIS and universities are investigating and
refining IPM tactics. One tactic uses trap logs: They let Tomicus breed,
but offspring are killed before they can leave the galleries.
This predatory beetle, Thanasimus formicarius, can eat
about three pine shoot beetles daily for up to 3 months.
Anti-breeding measures will be impractical, however, if the pest spreads to
America's vast tracts of forests and pine plantations. Here, natural enemies
could play a major role. They usually do control T. piniperda in its
native rangefrom Portugal to Japan, and from the Arctic Circle to the
Mediterranean. But in the United States, overwintering Tomicus
adults emerge 4 to 8 weeks before native predators and parasites.
The European beetle, Thanasimus formicarius, has better timing. While
Tomicus hunts for gallery sites, Thanasimus hunts for
Tomicus. And, in bark crevices near Tomicus galleries, a
female Thanasimus lays her eggs. She typically lays 160 to 310 over her
lifetime. The larval offspring raid the galleries, eating Tomicus eggs,
larvae, and pupae.
Dysart recruited Thanasimus almost every week last summer in a
crucial early stage of a cooperative biocontrol project by ARS, APHIS, and the
Forest Service. In the Lodeve Forest 45 miles from Montpellier, Dysart built
waist-high stacks of fresh-cut pine logs. He topped the stacks with fresh pine
branches and boughs.
Piney vapors attracted Tomicus and other bark beetles. They also
served as chemical dinner bells for T. formicarius. "We shook the
pine boughs over a sheet and picked up Thanasimus beetles that fell
off," he says. "Apparently, they rest on the boughs while waiting to
ambush arriving bark beetles."
Dysart sheltered some of the pine stacks with mesh-sided tents. From the
netting, he plucked dozens of Thanasimus insects during his weekly
rounds at Lodeve.
By summer's end, he had shipped more than 400 Thanasimus adults to
ARS' Beneficial Insects Introduction Research Laboratory in Newark, Delaware.
Quarantine officer Larry Ertle sent the immigrants' eggs and larval offspring
to APHIS' National Biological Control Laboratory in Niles, Michigan.
There, APHIS entomologist David Prokrym and colleagues have been nursing the
insects to adulthood, to set up supply lines to East Lansing.
"We're conducting lab studies to evaluate this European predator, and
we may test-release it outdoors in 1997," says Haack, the Forest Service
"First we want to gauge what effect the newcomer might have on native
insects, especially on our native natural enemies of pine bark beetles."
By Jim De Quattro, ARS.
Richard Dysart is at the USDA-ARS European Biological Control Laboratory,
Robert Haack is at the
USDA Forest Service, North Central
Research Station, 1407 S. Harrison Road, Room 220, East Lansing, MI 48823;
phone (517) 355-7740; ext. 108, fax (517) 355-5121.
"The Grinch That Spoils Christmas Trees" was
published in the December 1995 issue of
Agricultural Research magazine.