GYPSY AND BROWN-TAIL MOTHS AND THEIR CONTROL 9 



short interval during the growing season, but retardation of growth 

 and less wood result. 



Trees that are weakened by defoliation are susceptible to secondary 

 injuries by fungi and bark borers. From 1912 to 1915 heavy mor- 

 tality was noted among oaks that had been defoliated by the gypsy 

 moth, and this was followed by an outbreak of the two-lined chestnut 

 borer (Agrilus bilineatus Weber), whose larvae fed beneath the bark 

 of the weakened trees. During recent years this beetle has not caused 

 noticeable damage, but such a condition might recur without warning. 



The importance of tree growth in aiding retention of moisture in 

 the soil and preventing erosion, particularly in rugged country, is 

 well recognized. Defoliation encourages evaporation of moisture 

 from the soil during the most critical growing period in the summer, 

 renders such areas more susceptible to forest fires, and undoubtedly 

 diminishes the flow of small streams, some of which furnish the water 

 supply for reservoirs maintained for commercial or city use. The 

 money value of these losses cannot be readily computed. 



Defoliated or dying trees along roadsides and streets in residential 

 areas are objectionable, and the removal of trees from such locations 

 is a distinct loss to the community and the public in general. Recrea- 

 tional areas are being used to a greater extent each year, and here 

 the value of trees far outweighs the commercial value of the timber. 

 Ragged foliage and denuded trees, accompanied by crawling cater- 

 pillars, are avoided by the public. Trees in such locations have more 

 of a struggle for existence than trees that grow in natural environ- 

 ment without interference by man, and they therefore require added 

 protection. The increased interest in natural playground develop- 

 ment in New England and New York State seems to warrant more 

 than ordinary expenditures to preserve the trees for their esthetic 

 value alone. 



Figures 4, 5, and 6 illustrate the results of gypsy moth feeding in 

 various types of stands. 



FOOD PLANTS 



Unlike many leaf-eating insects, which confine their feeding to a 

 single species or group of plants, the gypsy moth is a general feeder 

 on trees and shrubs. In fact, in heavy infestations few species of 

 trees are ignored, especially by the larger larvae, and when food is 

 scarce grass and cultivated crops are sometimes eaten. 



A study of the food plants of the gypsy moth in 1913 3 revealed 

 distinct differences in the preferences of the very small and the larger 

 larvae. The food plants were grouped in four classes, which are 

 given herewith, with a few changes that subsequent observations have 

 justified. This classification can be used as a basis for thinning to 

 eliminate the most favored species and retain and encourage the more 

 valuable and resistant species. It will be noted that class 2 includes 

 most of the conifers, which suffer severely if grown in association with 

 more favored species. Unfortunately, the infested region abounds 

 in class 1 trees either in solid stands or in more or less diluted mixtures. 



» MOSHER, F. H. FOOD PLANTS OF THE GIPSY MOTH IN AMERICA. U. S. Dept. Agr. Bull. 250, 39 pp., illuS, 

 1915. 



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