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CONTROL OF GIPSY MOTH BY FOREST MANAGEMENT. 3 
the new foliage appears in the spring and stop before the middle of 
July. A gipsy-moth colony may exist for several years in a wood 
without doing sufficient damage to attract any attention. The mem- 
bers of such a colony multiply in numbers continuously and spread 
over more and more territory until ultimately a point is reached 
where the caterpillars suddenly become so abundant that they de- 
foliate large numbers of trees, frequently over wide areas. 
Following a gipsy-moth defoliation over a considerable area, the 
intensity of an infestation generally diminishes. This is due largely 
to the following causes: (1) Caterpillars die of starvation or migrate 
en account of the exhaustion of their food supply. (2) An epidemic 
of the wilt disease destroys large numbers of the insects. (3) Natural 
enemies, particularly parasites and predacious beetles, reduce the 
infestation. 
Woods which have suffered a heavy. gipsy-moth attack are thus 
usually provided with some opportunity to recover. A few cater- 
pillars survive in such cases, and in the course of a few years (three 
to five) defoliation again occurs. There is usually very heavy feed- 
ing following a season of defoliation if it happens, as it may occa- 
sionally, that an infestation is of such an extent that the amount of 
foliage available is just sufficient to carry the caterpillars to the 
pupation stage. 
An infestation once established in a wood will probably remain 
as long as the food supply lasts, but the degree of infestation will 
vary from time to time. 
The development and extent of gipsy-moth infestations are influ- 
enced to a large degree by meteorological conditions, insect enemies, 
and the wilt disease. Owing to the uncertainty with which these 
factors act, it is impossible to make a definite prediction as to the 
exact outcome of any infestation. 
Feeding occurs in varying degrees over all the infested region, 
the extent in any locality depending on the stage of the infestation 
and the character of the food. After defoliation most trees 1mme- 
diately put forth new foliage, and in a few weeks there is usually 
but little external evidence of damage. In such cases the injury 
amounts only to a temporary retardation of development, and from 
this the trees attacked usually recover. Trees previously weakened 
through the action of decay, fire, or poor growing conditions may 
not survive one defoliation, but mortality through this cause is low. 
Gipsy-moth feeding does not cease until after most of the early 
summer rains have fallen, so that defoliated trees in their weakened 
condition encounter more or less unfavorable conditions for their 
| recovery. An unusually dry summer may influence recovery very 
adversely. Defoliation by gipsy-moth caterpillars usually occurs 
