Torrey Pines Are Spared as Beetles Take the Bait : Sex appeal: Traps with chemical lure halt the ravages of beetles that killed many of the rare trees.

Scientists and park rangers announced Wednesday that a program using synthesized insect sex chemicals as bait appears to have halted the invasion of a tiny bark beetle that has ravaged hundreds of San Diego’s famous Torrey pines.

At a Wednesday-morning press conference at the Torrey Pines State Reserve south of Del Mar, officials said a five-month program has proven successful in baiting the pesky bugs into tubular traps.

Scientists say the tactic has proven a fatal attraction for the bugs, leading them to their own demise and eliminating any resort to pesticides, which are banned in the park.

The beetle has brought devastation to sections of the picturesque colony of gnarled pines.

With their narrow coastal habitat stretching only 4 miles along the coastline just north of La Jolla, the Torrey pines have long been known as San Diego’s home-grown wonders, the rarest species of pine in the county. The reserve is the only natural grove of the trees on the mainland United States.

But, three years ago, something began killing the stately trees. Ips paraconfusus , a tiny, short-sighted pest dubbed the “confused five-spined beetle” because of the aimless path it bores under the bark of its host, had invaded the park by the hundreds of thousands.

Eventually, aided by years of drought that weakened the tree’s defenses against their work, the beetles killed more than 15% of the reserve’s 7,000 Torrey pines, especially along the once-picturesque Guy Fleming, Razor Point and Parry Grove trails, transforming them into a devastated graveyard of twisted trunks and lifeless limbs.

“A profound sadness just took over this park as soon as we found out the trees were dying,” said Bob Wohl, supervising ranger at the reserve. “Many of these Torreys are beautifully sculptured. People would come and sit beneath their favorite tree and just meditate. To see them die like that was like losing members of the family.”

Under the direction of Patrick Shea, a research entomologist with the U.S. Forest Service, park staffers in May began setting a series of cone-shaped traps baited with synthesized beetle pheromones, or sex-attracting chemicals.

Now, the same chemicals that in their natural form attract tens of thousands of bark beetles to prey on a single pine are being used to lure the insects into the 5-foot-long traps, where they are collected by scientists.

When he began the “trap-out” program this spring, Shea said, he counted at least 33 trees that had recently been infected by the bugs, which can colonize and doom a tree within hours.

“In 25 years as an entomologist, I have never seen this beetle kill trees with this kind of intensity,” he said. “I’ve seen them take a spot of trees here or there. But never with this type of devastation.”

Since the traps were set, scientists have captured more than 200,000 beetles with the pheromones, which emit a smell much like turpentine. In the initial stages of the program, researchers collected as many as 29,000 of the bugs per week. Now, that number is down to fewer than 100. And only one new tree has become infected.

“I can’t come up with any other reasonable explanation (for the improvement) other than to say that the trap-out program is doing its job,” Shea said. “The beetles should have continued to move onto new trees. And they didn’t.”

Shea said the trap-out system now might be used in Northern California, especially in the western slopes of the Sierra Nevada range, where several species of pines have fallen victim to bark-burrowing insects.

For local rangers, the battle against the beetle has been a high-stakes and very frustrating race against time and nature.

Following strict park policies encouraging a laissez-faire management approach to help maintain the ecosystem of the reserve, they rejected such tactics as insecticides or artificial watering.

Meanwhile, the Torrey Pines kept dying--at first by the scores and, finally, by the hundreds.

“This park represents the last Torrey pine ecosystem on the mainland United States,” Shea said. “Sure, there are ornamental trees up and down the coast. But this was a very unique situation--the last stand for the Torrey pine.”

Torrey pines grow naturally in only two places in the world--in what is now the reserve and on Santa Rosa Island off the coast of Santa Barbara. Scientists say the foggy coastal climate maintains a thermal blanket that retards evaporation and moisture loss, making the trees thrive.

Once known as the soledad pine, the trees were renamed in 1850 by Dr. C.C. Parry, a botanist for the U.S.-Mexico Boundary Survey. Parry chose the botanical name Pinus torreyana , or Torrey pine, in honor of his former botany professor, Dr. John Torrey.

In 1899, heeding Parry’s argument that the trees were headed for certain extinction, the city of San Diego designated 369 acres of coast north of La Jolla as public parkland.

Philanthropist Ellen Browning Scripps acquired adjacent groves in the years that followed and the park had swelled to nearly 1,000 acres in 1924. A half century later, a 154-acre extension was formed on the sloping hillside to the north of Penasquitos Lagoon.

Scientists say the recent attack of killer bugs coincides with a storm during the winter of 1988 that felled more than two dozen trees. The beetle, which prefers feeding on downed wood, ravaged the dead trees.

Eventually, those weakened and fallen trees served as incubators for the beetle, which is less than a quarter of an inch long, with a dark brown body and tiny antennae with rounded ends.

Usually slow-moving, the winged insect is normally capable of wandering among several trees in a lifetime. But, once a host tree is located, the insects, employing their sexual attractant, can lure thousands of bugs to doom an otherwise-healthy tree in an afternoon.

Together, the insects hollow out a larval chamber in the tree, where the females lay their eggs. It is the hatched larvae that do most of the lethal damage, burrowing a tortuous course through the Torrey’s cambium layer, the soft level just beneath the bark that pumps nutrients throughout the tree.

By the summer of 1990, the ravenous beetles had eaten through a 20-acre swath of trees along the western slope of the reserve--aided by several summers of drought. The lack of water, scientists say, retarded the flow of sap that normally repels the invading hordes, pushing their eggs out or encasing an attacker in a coat of resin.

Local rangers and park visitors watched helplessly as their favorite trees withered. Especially in the reserve’s North Grove section, the infestation turned trees from a healthy green to yellow and then brown and, finally, to a rusty red as the Torreys dropped their needles by the tens of thousands.

Bill Tippits, a state park ecologist, said that, in recent decades, the Torreys had endured two other minor attacks, which wiped out scores of trees but reached nowhere near the extent of the recent infestation. “Our experience was that a small number of trees died until, as a whole, the trees’ natural defenses took over. But that wasn’t happening this time.”

Then the rangers learned of Shea’s research with pheromones.

“It was just kind of serendipitous that we got together,” Shea said. “I was doing this research, and all the while they were under attack by people because they weren’t acting fast enough to save the trees. It wasn’t a matter of not responding. They had to find the right way to battle the problem.”

Now, park rangers will begin a program to replenish the devastated areas of the reserve. In December, rangers will conduct a controlled burn of 5 acres in the North Grove section--an area that will then be reseeded.

For rangers like Bob Wohl, the apparent victory over the bark beetles ends a discouraging period of disappointment for park visitors who watched as their their favorite specimens died limb by limb.

“They’d come running up to our office saying, ‘What on earth has happened to our favorite grove of trees?’ ” he said. “They wanted us to do something , anything, even if it was going out there with hammers to kill those bugs.”

On patrols around the reserve, Wohl feels a sense of victory tinged by remorse.

“Sure, we halted the rush of dead trees,” he said. “But there’s a certain sadness that it had to go that far. Each and every one of those trees were individuals, they had unique personalities, the way they grew.

“And so, all of us, we lost a lot of our favorite trees. They aren’t redwoods, they won’t live to be 1,000 years old--just 200 years or so. We knew they were going to die someday. But selfishly, I guess, we wanted them around for our lifetimes.”