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 

 on 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 imme- 

 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 fallenj 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 



