pounds of lime and 80 pounds of sulfur, in 50 gallons of water.  It
    may be had in prepared form and should then be used at the rate of 1
    gallon to about 9 gallons of water in winter or early spring before
    the buds open.  At other times of the year and for the softer-bodied
    insects a more diluted mixture, possibly 1 part to 30 or 40 parts of
    water, should be used, varying with each case separately.

  Kerosene emulsion consists of one-half pound of hard soap, 1 gallon
    of boiling water, and 2 gallons of kerosene.  It may be obtained in
    prepared form and is then to be used at the rate of one part of the
    solution to nine parts of water when applied in winter or to the
    bark only in summer.  Use 2 gallons of the solution to a 40-gallon
    barrel of water when applying it to the leaves in the summer. 
    Kerosene emulsion is useful as a treatment for scale insects.

  Tobacco water should be prepared by steeping one-half pound of
    tobacco stems or leaves in a gallon of boiling water and later
    diluting the product with 5 to 10 gallons of water.  It is
    particularly useful for plant lice in the summer.

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.

All insects develop from eggs, Fig. 99.  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