In this day of Space discovery, it is paradoxical that we still know and understand so little of our earthbound world, in particular the vast world of lifeforms we know as insects. And our knowledge is tinged with ignorance which should embarrass us, but does not. We cannot help considering insects to be loathsome and, to some, frightening.
There are even “bug zappers” on the market which attract and electrocute insects indiscriminately, as humans thoughtlessly annihilate a positive link in the natural chain. Such prejudice belies the human frailty of easy generalization. Insect equals bad, in the way that foreigner equals threat.
We exclude butterflies, of course, and lightning bugs (which are also beneficial). The “good” insects work in either of two ways: as predators of other insects or as parasitic, usually through eggs which become larvae feeding on pest insects.
Here are some desirable insects, offered in the hope that familiarization will lead to understanding, which will lead to better gardening.
The Lady beetle (Coccinellidae), sometimes called “Ladybird” and “Ladybug,” is popularly admired as cute and harmless. It is also a voracious feeder upon damaging insects, of so much benefit that it was originally called Our Lady’s beetle. Both the adult beetle and the larva destroy aphids, mites, mealybugs, scales, and other tiny insect pests.
In spring, the adult emerges from hibernation under garden litter, or it hatches from a pupa on a tree branch or leaf. In five to 13 days, each female attaches as many as 1,500 orange eggs onto garden leaves. Those not eaten by predators reach maturity in two or three weeks, so many generations appear over the growing season.
You can buy Ladybugs by the pint through the mail, and you cannot force them to stay in your own garden when there are better eats next door. But that would be an indication that you do not have a significant aphid problem.
On the subject of “pleasant” insects, the Green Lacewing (Chrysopa carnea) certainly sounds agreeable. And seeing them in the garden is even more gratifying when we know what good they do. For each one can eat as many as forty garden pests--primarily aphids and mealybugs-- an hour.
Lacewing larvae, called aphid lions, suck body fluids from red spider mites, thrips, leafhoppers, and aphids. They are voracious as soon as they hatch, sometimes piling victims on their backs as they work. Several generations may occur in the garden during the year.
Dragonflies (Odonata anisoptera) whiz around at sixty miles an hour, catching as many as 100 mosquitoes a day. They also like beetles, moths, flies, termites, and other pest insects, catching them all on the wing.
They like to be around water, so a birdbath or other water source is desirable in or near the garden. In fact, in the fall they lay eggs on water plants or on the water’s surface, and the young swim underwater, catching tadpoles, minnows, and mosquito larvae.
They overwinter as nymphs, sometimes taking two years to reach maturity. When dragonflies are seen in the garden, it is helpful to provide perches, such as short bamboo stakes, here and there, where they can survey their smorgasbord.
Damselflies (Odonata zygoptera) resemble dragonflies, except that their wings are folded together above the back, not extended horizontally. They are smaller than dragonflies and fly much slower; and they are amazingly predaceous for their size.
For a checklist of local dragonflies and damselflies, see the Howard County Bird Club link.
This species should not be confused with the Damsel bug (Nabidae), which is small (less than 1/2 inch long), gray or brown in color, and able to fly long distances. It can usually be found on low vegetation.
A member of the True Bug family, it preys on a wide range of garden pests, including aphids, caterpillars, leafhoppers, thrips, and other plant-eating True Bugs. They pierce their victims and suck fluid from them.
Damsel bugs lay their eggs in plant tissue. After they hatch, the nymphs start to feed on whatever prey is available.
Arguably the best-known beneficial insect is the Praying Mantis (Mantis religiosa). This fascinating creature is even the subject of several Internet homepages, some of them serious, some fantastic.
It is a relatively “good” insect, in that it devours many garden pests, but unfortunately it will also go after all the other beneficials we have tried to encourage.
Since it grows to be very large (as long as four inches) and looks so menacing, it is worth allowing to exist in the garden, if only for entertainment. The mantis also provides interest for children who may be just beginning to explore nature and its workings.
One more beneficial insect which should be better known, or at least recognizable in the garden, is the Assassin bug (Reduviidae). There are more than 100 species in North America, feeding on flies, mosquitoes, beetles, caterpillars, and many other pests. They are also True Bugs, which include Squash bugs, Tarnished Plant bugs, and Harlequin bugs, which Assassins also devour.
Adults have a flattened oval shape with a conical head and a curved beak. They measure an inch long, with longer legs than those of destructive bugs.
These bugs can inflict a nasty bite, so shake plants before harvesting or cutting, to send the bugs into hiding.
Other beneficial insects are wasps of all sorts, yellowjackets, and honeybees. Everyone knows that they can sting when aroused; thus the experienced gardener knows to walk away. And it is imprudent to try to eradicate these helpers. Anyway, most of the time a bee or wasp will sting when there is nothing else it could do.
Of special interest is the parasitoid Braconid wasp (Braconidae), which lays its eggs on the Tomato Hornworm.
The eggs feed on the worm, eventually killing it and producing more beneficial wasps. So, when observed on tomato plants, do not interfere. Let nature take its course. Only a little of the tomato plant will be lost, ultimately.
There are many other beneficials, of course; but the ones described are readily recognizable in most vegetable and flower gardens. Seeing them in our garden landscapes suggests successful biological controls and that chemicals may be unnecessary. They also help to illustrate the truism that four out of five insects are beneficial in the landscape and to demonstrate the essential truth of the balance of nature when man cooperates in an educated and sympathetic way.
--Peter Van Egmond, MG, January 1997
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