North Coast Journal

GARDENING - JUNE 1995
Terry Kramer

Good bugs, bad bugs

If there is one garden insect that can make my blood boil, it is the aphid, especially after finding many little carcasses sprinkled in the kitchen sink after I've cooked and eaten some "organic" broccoli. This ubiquitous little garden creature is a real nuisance when left to have its way with plants.

Of all pests, aphids are the most widespread and prolific. With more than 4,000 known species of aphids, there is nary a plant in this world that can escape its attack.

Commonly called by gardeners aphis, greenfly, blackfly, plant louse and an assortment of four-letter words, aphids are an interesting and colorful lot. Their tender bodies can be green, black, orange, rosy-pink, wine-red, white, grey and even lavender.

The different species even have colorful names such as the rosy-apple aphid (rosy brown), the golden-glow aphid (bright red) and the crescent-marked lily aphid (yellow with a black U-shaped patch on its back). Most aphids are from 1/16 inch to 1/8 inch long.

Depending on the species, aphids attack all parts of plants, including leaves, flowers, stems, bark, fruit and roots, as well as tender, nubile shoots. They are soft-bodied, pear-shaped insects that suck the life juices from a host. When an aphid injects its slender, hollow proboscis into a favored plant part, it immediately beings depleting the plant's sap.

From out of its back end, the aphid secretes honeydew, a sugary excretion that ants love. In fact, aphids are sometimes called "ant cows" because ants herd them about, milking the sticky honeydew from their bodies.

If you have ants crawling around your plants, chances are you have an aphid infestation. Honeydew secretions also foster a damaging black fungus called sooty mold, which is commonly seen on camellias, birches and citrus.

When it comes to having babies, aphids are the most prolific of all insects, really. They are born pregnant. Females reproduce without being fertilized by males, and they bear all-female offspring that can produce another generation of females in a mere six days.

If a single female aphid had a perfect life, she could produce five billion offspring in one season, aphid experts estimate. Males are only available in the autumn when the lower light levels of this time of year trigger the birth of males. They mate with female aphids to produce overwintering eggs.

Allowing aphids to multiply excessively in the garden is bad for a number of reasons, beside rendering edible crops unappetizing. Damaged plants wilt, become deformed and stunted. First signs of aphid infestation are usually curled, mottled leaves. Aphids not only damage plants, they also transmit viruses, especially the dreaded mosaic virus. And then there is the sooty mold.

So, if aphids are such awful plant insects, why do they exist, you might wonder. This is because there are quite a number of natural predators that need aphids to survive. Ladybugs, for example, are voracious consumers of aphids.

Did you know that a single ladybug larvae can eat at least 40 aphids in just one hour? The assassin bug will suck the life juices out of an aphid.

Braconid wasps take advantage of aphids by laying eggs inside of them. Eggs hatch and the larvae grow inside the aphid, weakening and killing it. Chalcids do the same thing.

The lacewing, or aphid lion, is a vicious predator of aphids. Seizing an aphid in its tusklike jaw and lifting it high off the plant, the aphid lion sucks it dry. Other aphid eaters include the praying mantis, the minute pirate bug, the soldier beetle, the rove beetle, the aphid midge and the syrphid fly.

But aphids are not without their own devices to fool a predator. When aphids feed on a plant, the leaves often curl up around the thriving colony, making a safety shield from sprays and predators. Some species of aphids produce galls on the plant that serve as protection.

Studies by entomologists at Texas A & M have revealed that when the bodies of some aphids are crushed, or damaged, they release a scent that alerts other aphids nearby to flee from danger.

The best way to keep aphids under control is to invite predators into your garden. You can accomplish this by planting plants that predators like.

For instance, marigolds attract syrphid flies. Pollen-producing plants like clover, daisy, dill, fennel and yarrow, dandelion, Queen Anne's lace, evening primrose and lamb's quarters offer pollen and nectar to lacewings. Parasitic wasps are attracted to fresh water.

Many aphid predators can be purchased by mail order and released into the garden. But this is a tricky business, because some - like ladybugs - will simply fly away if environmental conditions are not just right for them.

Aphids can also be controlled with other methods. Insecticidal soaps containing potassium salts (Safer's) that smother aphids, are readily available at most garden centers. This type of soap is nontoxic to humans, animals and beneficial insects. During the dormant season, it is a good idea to spray fruit trees and deciduous shrubs with a horticultural oil. It will smother aphid adults and eggs.

Botanic insecticides are made from natural plant materials and break down quickly into harmless substances. They are not, however, completely safe to the people or beneficial insects. Pyrethrum, made from the crushed dried flowers of a member of the chrysanthemum family, kills aphids, but it's also toxic to fish, honeybees and people.

Rotenone is derived from the roots of the tropical plant Derris and is toxic to people. Quassia and Sabadilla are two somewhat safer botanics that can be used to control aphids. Care must be taken when using botanics.

Simply strolling through the garden a couple times a week to inspect aphid-prone plants will allow you to keep populations in check. It is also fun. If you see aphids, hose them down with a blast of water. Squirt them with insecticidal soap.

Before finding out about the Texas A & M study, I used to like to cruise my yard and, using my thumb and forefinger, squish any aphids that I found collecting at succulent new shoots and flower buds. Now I look for wild ladybugs crawling on Queen Anne's lace so I can catch them and put them on the broccoli seedlings.

 

Terry Kramer is a Bayside free-lance writer and the owner of Jacoby Creek Nursery.

 



Comments on this story? E-mail the Journal: ncjour@northcoast.com

The North Coast Journal Table of Contents

North Coast Journal weekly banner