THE COASTAL GARDENER:

Last week, I received a desperate call from a gardener in Newport Beach. I’ll call her “Fran,” since she was frantic about her situation. She described on her roses a terrible-looking bug, which must have been up to no good. It was black and orange, with bumps and prickles. Fran had already done some Internet research and looked through the labels on her arsenal of bug sprays, but could not figure out what these terrible monsters were.

“How do I get rid of them?” she asked. “I’m not sure what they are, but I need to know how to get rid of them.” An hour later she arrived at the nursery, pacing nervously, with a plastic bag in her hand. In her clutch were a few leaves and an example of one of the hideous invaders.

As I suspected, the “monster” turned out to be one of the “good guys.”

By now, just about everyone knows that ladybugs, more properly called lady beetles, are beneficial insects. But there are still a few who do not understand the careful balance of pest to prey that is always at play in a healthy garden. Fran’s monsters were immature lady beetles.

Lady beetles are among our most beneficial insects, consuming huge numbers of plant-feeding pests, mostly aphids, but also scale and mealybugs. The French call them les bêtes du bon Dieu, or creatures of the good God, and les vaches de la Vierge, or cows of the virgin. Germans call them Marienkäfer, or Mary’s beetles. Gardeners should call them friends.

Like all beetles, lady beetles have a complete metamorphosis. Remember from school, the egg, larva, pupae and adult stages look quite different from each other. Females deposit eggs in clusters of up to a dozen. The larvae hatch in about a week and immediately start consuming aphids or other pests. In a little less than a month, they pupate; about a week later, the adults emerge and feed again on aphids and other pests.

The appetite of lady beetles is remarkable. An adult may consume up to 75 aphids a day, equaling its own body weight every 24 hours. And the larvae that Fran was so anxious to eliminate are even hungrier, eating up to 350 aphids during their brief span.

Lady beetles are, of course, an example of biological pest control. In addition to predators like lady beetles, lacewings and decollate snails, biological control includes parasites, pathogens and competitors, all controlling pests and their damage. Collectively, these good guys are called “natural enemies.”

Distinguishing plant pests from natural enemies is an important lesson for a gardener, and I tried to impress upon Fran that these were desirable companions in her rose garden. Fran seemed skeptical, but listened to my explanation.

In a healthy garden, naturally occurring beneficial organisms should be conserved and encouraged. Most pests are attacked by several different natural enemies, and conserving these is the most effective way to successfully use biological control in a garden.

Conversely, broad-spectrum pesticides often kill a higher proportion of natural enemies than the pests they are applied to control. They may also leave residues that kill natural enemies, which migrate in later. Even if natural enemies survive a pesticide application, residues can interfere with their reproduction and ability to locate and kill pests.

If we want to encourage lady beetles and other natural enemies, eliminating or reducing the use of broad-spectrum, persistent pesticides whenever possible is a good place to begin. Many broad-spectrum insecticides (especially carbamates, organophosphates and pyrethroids) are especially toxic to these good guys.

If pesticides are still used, apply them in a selective manner. Choose insecticides that are specific to the pest they are designed to control and choose ones with little or no persistence, like insecticidal soap, horticultural oil, natural plant oils and others.

I’m not sure whether Fran was convinced by my explanation. She wanted badly to do something; spray something. So I took the little “monster” and, after she left, I carefully put it onto a plant at the nursery. Some people just don’t get it.

RON VANDERHOFF is the nursery manager at Roger’s Gardens in Corona del Mar.