STUDY 1. INSECTS: THE LIFE HISTORY OF AN INSECT

In a general way, all insects have four stages of transformation before a new generation is produced. It is important to consider the nature of these four stages in order that the habits of any particular insect and the remedies applicable in combating it may be understood.

1. All insects develop from eggs.



The eggs then hatch into caterpillars or grubs, which is the larva stage, in which most insects do the greatest damage to trees. The caterpillars or grubs grow and develop rapidly, and hence their feeding is most ravenous.

Following the larva stage comes the third or pupa stage, which is the dormant stage of the insect. In this stage the insect curls itself up under the protection of a silken cocoon like the tussock moth, or of a curled leaf like the brown-tail moth, or it may be entirely unsheltered like the pupa of the elm leaf beetle.

After the pupa stage comes the adult insect, which may be a moth or a beetle.

A study of the four stages of any particular insect is known as a study of its life history. The important facts to know about the life history of an insect are the stage in which it does most of its feeding, and the period of the year in which this occurs. It is also important to know how the insect spends the winter in order to decide upon a winter treatment.

IMPORTANT INSECTS - THE ELM LEAF BEETLE

Life History: The elm leaf beetle is annually causing the defoliation of thousands of elm trees throughout the United States. Several successive defoliations are liable to kill a tree. The insects pass the winter in the beetle form, hiding themselves in attics and wherever else they can secure shelter. In the middle of May when the buds of the elm trees unfold, the beetles emerge from their winter quarters, mate, and commence eating the leaves, thus producing little holes through them.

While this feeding is going on, the females deposit little, bright yellow eggs on the underside of the leaves, which soon hatch into small larvae or grubs.

The grubs then eat away the soft portion of the leaf, causing it to look like lacework.

The grubs become full grown in twenty days, crawl down to the base of the tree, and there transform into naked, orange-colored pupae.

This occurs in the early part of August. After remaining in the pupa stage about a week, they change into beetles again, which either begin feeding or go to winter quarters.

Remedies: There are three ways of combating this insect:

1. First, by spraying the foliage with arsenate of lead (Note: A different insecticide must be used in modern times. Lead arsenate was officially banned as an insecticide in the US on August 1, 1988.) in the latter part of May while the beetles are feeding, and repeating the spraying in June when the larvae emerge. The spraying method is the one most to be relied on in fighting this insect.
2. A second, though less important remedy, consists in destroying the pupae when they gather in large quantities at the base of the tree. This may be accomplished by gathering them bodily and destroying them, or by pouring hot water or a solution of kerosene over them. In large trees it may be necessary to climb to the crotches of the main limbs to get some of them.
3. The third remedy lies in gathering and destroying the adult beetles when found in their winter quarters. The application of bands of burlap or "tanglefoot," or of other substances often seen on the trunks of elm trees is useless, since these bands only prevent the larvae from crawling down from the leaves to the base and serve to prevent nothing from crawling up. Scraping the trunks of elm trees is also a waste of effort.

THE TUSSOCK MOTH

Life history: This insect appears in the form of a red-headed, yellow-colored caterpillar during the latter part of May, and in June and July. The caterpillars surround themselves with silken cocoons and change into pupae. The mature moths emerge from the cocoons after a period of about two weeks, and the females, which are wingless, soon deposit their eggs on the bark of trees, on twigs, fences, and other neighboring objects. These eggs form white clusters of nearly 350 individual eggs each, and are very conspicuous all winter.

Remedies: There are two ways of combating this insect:

1. By spraying with arsenate of lead for the caterpillars during the latter part of May and early June. (Note: A different insecticide must be used in modern times.)
2. By removing and destroying the egg masses in the fall or winter.

THE GYPSY MOTH

Life history: This insect, imported from Europe to this country in 1868, has ever since proved a serious enemy of most shade, forest, and fruit trees in the New England States. It even feeds on evergreens, killing the trees by a single defoliation.

The insect appears in the caterpillar stage from April to July. It feeds at night and rests by day. The mature caterpillar, which is dark in color, may be recognized by rows of blue and red spots along its back. After July, egg masses are deposited by the female moths on the bark of trees, and on leaves, fences, and other neighboring objects. Here they remain over the winter until they hatch in the spring. The flat egg masses are round or oval in shape, and are yellowish-brown in color.

Remedies: Spray for the caterpillars in June with arsenate of lead (Note: A different insecticide must be used in modern times.) and apply creosote to the egg masses whenever found.



THE BROWN-TAIL MOTH

Life history: This insect was introduced here from Europe in 1890 and has since done serious damage to shade, forest, and fruit trees, and to shrubs in the New England States.

It appears in the caterpillar stage in the early spring and continues to feed on the leaves and buds until the last of June. Then the caterpillars pupate, the moths come out, and in July and August the egg clusters appear. These hatch into caterpillars which form nests for themselves by drawing the leaves together. Here they remain protected until the spring.

Remedies: Collect the winter nests from October to April and burn them. Also spray the trees for caterpillars in early May and especially in August with arsenate of lead. (Note: A different insecticide must be used in modern times.)



THE FALL WEBWORM

The caterpillars of this insect congregate in colonies and surround themselves with a web which often reaches the size of a foot or more in diameter. These webs are common on trees in July and August. Cutting off the webs or burning them on the twigs is the most practical remedy.

THE LEOPARD MOTH

Life history: This insect does its serious damage in the grub form. The grubs which are whitish in color with brown heads, and which vary in size from 3/8 of an inch to 3 inches in length, may be found boring in the wood of the branches and trunk of the tree all winter. The leopard moth requires two years to complete its round of life. The mature moths are marked with dark spots resembling a leopard’s skin, hence the name. It is one of the commonest and most destructive insects in the East and is responsible for the recent death of thousands of the famous elm trees in New Haven and Boston.

Remedies: Trees likely to be infested with this insect should be examined three or four times a year for wilted twigs, dead branches, and strings of expelled frass; all of which may indicate the presence of this borer. Badly infested branches should be cut off and burned. Trees so badly infested that treatment becomes too complicated should be cut down and destroyed. Where the insects are few and can be readily reached, an injection of carbon bisulphide (Note: Use a modern treatment.) into the burrow, the orifice of which is then immediately closed with soap or putty, will often destroy the insects within.



THE HICKORY BARK BORER

Life history: This insect is a small brown or black beetle in its mature form and a small legless white grub in its winter stage. The beetles appear from June to August. In July they deposit their eggs in the outer sapwood, immediately under the bark of the trunk and larger branches. The eggs soon hatch and the grubs feed on the living tissue of the tree, forming numerous galleries. The grubs pass the winter in a nearly full-grown condition, transform to pupae in May, and emerge as beetles in June.

Remedies: The presence of the insect can be detected by the small holes in the bark of the trees and the fine sawdust which is ejected from these holes, when the insects are active. It is important to emphasize the advisability of detecting the fine sawdust because that is the best indication of the actual operations of the hickory bark borer. These holes, however, will not be noticeable until the insect has completed its transformation. In summer, the infested trees show wilted leaves and many dead twigs. Holes in the base of the petioles of these leaves are also signs of the working of the insect. Since the insect works underneath the bark, it is inaccessible for treatment and all infested trees should be cut down and burned, or the bark removed and the insects destroyed. This should be done before the beetles emerge from the tree in June.



PLANT LICE OR APHIDS

These often appear on the underside of the leaves of the beech, Norway maple, tulip tree, etc. They excrete a sweet, sticky liquid called "honey-dew," and cause the leaves to curl or drop. Spraying with whale-oil soap solution (Note: Use dish soap solution in modern times.) formed by adding one pound of the soap to five gallons of water is the remedy.