18 U. S. DEPARTMENT OF AGRICULTURE BULLETIN NO. 484. 



These stands were carefully selected after a thorough search of the 

 infested region to find stands having varying proportions of different 

 species, and they are typical of the region. 



It will be noticed that in the first four the Class I trees (favored 

 food of the gipsy-moth caterpillar) from 50 to 94 per cent of the 

 whole stand. It is obvious that in such cases any plan which pre- 

 scribes the remoA'al of all Class I trees involves a radical change in 

 composition and can not be efficacious unless the sprouts which follow 

 cutting are also removed. 



This classification of trees according to their susceptibility to attack 

 by the gipsy-moth caterpillar, though based upon careful experiments 

 in the laboratory and extended observations in the field, is not abso- 

 lute. In some cases it may have a direct bearing upon forest man- 

 agement in the region infested with the gipsy moth, but it is not 

 yet conclusive as to moth control, for there is a wide range, for exam- 

 ple, between the susceptibility of white oak and of beech, which 

 are both Class I trees. It is, therefore, subject to revision, if later 

 experiments or field observations should require it. 



OTHER FACTORS IN MANAGEMENT FOR MOTH CONTROL. 



A sound plan for moth control by forest management must be 

 based not only upon the susceptibility of the trees to attack by the 

 caterpillars and upon their silvicultural requirements as individuals 

 and as component parts of the stands in which they occur, but also 

 upon the degree of infestation. In the work of the Bureau the degree 

 of infestation b}' the gipsy moth is determined by counting the num- 

 ber of egg clusters, each containing from 300 to 500 eggs and laid by 

 a single female. 



The number of egg clusters per acre at any given date, while by no 

 means satisfactory, is the best standard as yet available by which to 

 compare the degree of infestation in different stands, or in the same 

 stand in different years. It is, of course, a better index of the de- 

 foliation to be expected the next year than of that which occurred 

 the year the eggs were laid, and as such becomes a factor in manage- 

 ment for moth control. It should be remembered, howeA'er, that 

 when very high figures are reached relief may reasonably be expected 

 from outbreaks of the wilt disease, 1 migration of the caterpillars, 

 attacks by parasites and other insect enemies, starvation, or other 

 natural causes. 



SOME CONTROLLING FACTORS IN MANAGEMENT. 



Since Mosher has concluded that " tray work and field observations 

 show that the white oak is probably the most favored food plant of 



1 Olaser, R. W., and Chapman, J. W. The wilt disease of gipsy moth caterpillars. In 

 Jour. Econ. Ent., v. 5, p. 479-488, 1913. See Bibliography, p. 487-488. 



