Killer Ladybugs

Why don't we begin with some important facts about the convergent ladybug. First of all, she is not a bug. She's a beetle. Second, she's not much of a lady. In the heat of the day, she tends to bite with unladylike ferocity. Third, the "convergent" part of her name refers only to the two converging white dashes on her thorax, not her tendency to gather in great teeming throngs. But "converge" is what the ladybug does best each summer when she and her fellow beetles (about half of whom are actually males) fly in from the heat-weary desert and aggregate on some of Arizona's most prominent peaks, where they seem content to wile away their time in great ladybug encampments, blanketing trees, rocks, and soil in flowing swathes of orange that can reach concentrations of 120 million ladybugs per acre. For six years, I lived in the middle of just such a prime ladybug encampment. It was located directly beneath my lookout tower in the Pinal Mountains of central Arizona. The ladybug presence there was not something to be ignored. At night a few of the more adventurous "ladies" would crawl in bed with me and tickle my legs. By morning my shoes might be filled with them. And in the afternoons, well, that was when the swarming ladybugs grew most active. Launching into the air by the millions, they would so clog the atmosphere with their hovering bodies that simply walking through them meant emerging sprayed with specks of orange from head to toe. What could possibly govern such bizarre behavior? "Simple," says entomologist Dave Langston. "It's the nature of the beast." Langston chuckles as he says this. After 15 years as an entomology specialist for the Cooperative Extension Service, he knows that most insect life is anything but simple, and the life of the convergent ladybug is no exception. It involves a curious blend of epic migrations, long hibernations, and a singular harmony that can only exist between two insect species one a predator and the other its prey. The prey in this case is the tiny white aphid, a well-known plant killer and the scourge of farmers and gardeners everywhere. And the predator? It is, of course, our lovable, bumbling, polka-dot-clad ladybug. As a hunter, she is ferocious, and, as an ally to gardeners, she is irreplaceable. Her story, according to Langston, begins and ends in the fresh green fields of spring. "Ladybeetles disseminate over the valleys in late February or early March," begins Langston, who prefers the purist term ladybeetle to the more common ladybug. "That is when aphids are most prevalent. The ladybeetles come from the mountains, find the aphids, and feed for a couple of weeks." Finding aphids is critical for the ladybug because only a steady diet of them will stimulate her reproductive system. Without aphids, in other words, the convergent

When aphids are attacking everything green in your yard, look to the sky for help. Mandibles at the ready, here come the KILLER LADYBUGS

ladybug as a species would cease to exist.

"When the female ladybeetles have consumed enough aphids," Langston continues, "they begin to lay eggs in small batches, on trees, shrubs, weeds, wherever they find high numbers of aphids. Afterward the adult ladybeetles die."

Their sudden departure might seem premature, leaving our gardens at the mercy of the remaining aphids. But this is not the case, says Langston. Reinforcements are on their way. Ladybug larvae will hatch in less than a week.

"What most people don't realize," says Langston, "is that ladybeetle larvae consume more aphids than the adults. They are like little dragons. Where an adult might eat 200 aphids in its lifetime, a larva will eat 600 aphids. So I tell people that the real benefit from ladybeetles comes after they lay their eggs. Unfortunately that is exactly when a lot of people want to spray for aphids. They don't realize that ladybeetles are still around because they don't recognize them as larvae." The confusion is understandable; a ladybug larva looks nothing like the adult. She is dark, wormlike, warty, and soft. But she does share a common trait with her mother: an enormous appetite.

To sate this appetite, each "little dragon" methodically stalks her quarry up and down the stems of green plants. When she literally bumps into a feeding aphid, she stops, pierces the victim's skin with her sharp mandibles, and sucks it dry. Then she moves on to her next victim.

In a matter of weeks, each hungry larva has eaten enough aphids to grow to her final larval stage. Then she stops feeding for a few days and enters the pupal stage. When she emerges, she is in her familiar adult form: shiny, round, orange, and usually punctuated by 12 black spots. At this point, she resumes her stalking behavior, but here comes the hitch. Because most of the aphids have been wiped out, food now is in short supply. So she departs.

"Unlike most ladybeetles, the convergents fly straight up," says Langston. "Straight up into the air until they reach a layer that is about 50° F. Then they either fly or let the prevailing winds carry them up to the mountains."

Inexplicably, the ladybugs seem to return to the same mountains every year. "Mingus, Four Peaks, the Mogollon Rim` areas, Mount Lemmon, Mount Wrightson, Mount Graham, Baboquivari. almost every major peak in Arizona is just loaded with them," says Langston.

But not every inch of every mountain is chosen as a landing site. Why not?

"No one knows," says Dr. Mont Cazier, entomology professor emeritus at Arizona State University. But aphids, he says, are definitely not a factor because there are insufficient aphids in the mountains to support a massive ladybug migration. Instead, Cazier says, certain environmental conditions may attract the ladybugs: specific temperatures, humidity, or a suitable solar exposure. On the other hand, he admits, odors left from last year's ladybugs may key the first arrivals into a particular area. "Whatever it is," Cazier says, "as soon as one ladybug lands on a peak, it draws others to it like a beacon. That is their instinct, to stick together."

In the mountains, the convergent ladybug takes on a new life-style. Here, short on aphids, she turns to such alternative fuels as pollen, which provides a rich, readily available food source. But unlike the aphid diet, pollen fails to stimulate reproduction. Instead, it appears to trigger sleep-inducing hormones. "The ladybug's whole physiology changes in the mountains," says Carl Olson, an entomology taxonomist at the University of Arizona. "Things inside their bodies shut down. They enter a dormancy period estivation. It is like hibernation, only it takes place during the summer."

When they are ready for estivation, ladybugs gather in astonishing masses. The sheer weight of their bodies flattens the bushes on which they sit. They cluster in such numbers they can easily be scooped up by the handful. "Selling ladybugs used to be a scam," says Olson. "People collected them in the mountains, brought them down, sold them to gardeners, and then the ladybugs went right back up again because they weren't hungry. You see, the ladybugs' systems have already turned off to feeding, turned off to mating, turned off to any of that stuff. All they want to do is get back up to that mountain they came from. So the ladybugs sleep, and they sleep safely, their orange bodies and musty odor warding off predators. But a combination of prolonged heat and the onset of summer rains can wake them from their slumbers and send them flying aimlessly. It also appears to make them irritable. When they bump into a human, they will dig in and take a tiny bite, but it is only a sharp pinch that leaves no mark or itch.

As summer wanes and cold weather sets in, the ladybug's aimless flights become less frequent, for now she faces winter hibernation. By November our beetle will have found shelter with a few million of her closest companions. There she tucks her head snugly under the belly of her neighbor and falls asleep.

At some point in February, a brief winter thaw will signal the ladybugs to awaken and mate. This mating strategy, some entomologists believe, may be the primary reason why the convergent ladybug gathers in such great concentrations in the mountains. Finding herself conveniently situated amidst millions of her kind, she need waste little time searching for a suitable mate. Later, when the ladybug discovers she is hungry again, she leaves the mountaintop, fies down to the fields of her birth, fills her belly on aphids, and lays her eggs. From those eggs will emerge progeny that will continue the instinctive quest for aphids.

Even with this wholesale slaughter going on each year, it may appear to many a backyard gardner that ladybugs have little effect on aphid populations.

But they do, responds Dave Langston. "Aphids, you see, are like little Xerox machines. They bear living young, all females, all exact duplicates of themselves, all with a tremendous reproductive capac-ity and, most important, all with a tremendous capacity to damage plants. Without ladybugs and other natural predators to eat aphids, they would have a devastating impact on fruit crops and urban plantings. If aphids ran wild in March, for example, our yards would be decimated by April."

For just that reason, entomologists suchas Langston try to keep people from inadvertently wiping out our ladybug friends. "For years we have been working to educate both growers and gardeners not to spray, spray, spray with pesticides," says Langston. "We try to teach people to man-age aphids instead. For one thing, we tell them that there is a threshold level below which you can have aphids without dam-age to plants. And even if you pass that threshold, it doesn't mean you should automatically spray. First see if ladybeetles are in the area. If not, find out if they are on their way. If so, let them do their job. Later, if you still need to spray for aphids, you can do it after the ladybeetles and their larvae are gone. We recommend a mix of liquid detergent and water. Pesticide use is only a last resort."

as Langston try to keep people from inadvertently wiping out our ladybug friends. "For years we have been working to educate both growers and gardeners not to spray, spray, spray with pesticides," says Langston. "We try to teach people to manage aphids instead. For one thing, we tell them that there is a threshold level below which you can have aphids without damage to plants. And even if you pass that threshold, it doesn't mean you should automatically spray. First see if ladybeetles are in the area. If not, find out if they are on their way. If so, let them do their job. Later, if you still need to spray for aphids, you can do it after the ladybeetles and their larvae are gone. We recommend a mix of liquid detergent and water. Pesticide use is only a last resort."

With a little bit of human care, says Langston, our lovable convergent ladybug will continue to protect our gardens each spring, then fly away to the mountains where she will drape the summer landscape in orange.