16 IMPROVEMENT THINNINGS IN 



THINNINGS IN GYPSY AND BROWN-TAIL 

 MOTH WORK. 



Thinnings are a logical development in the fight against the 

 gypsy and brown-tail moths. However, thinnings as made in this 

 work differ considerably from the improvement thinnings pre- 

 viously mentioned, and perhaps some other term should be used to 

 describe them. They vary all the way from what practically 

 amounts to clear cutting to merely the chopping out of underbrush 

 and dead trees. 



METHODS OF MOTH CONTROL. 



Some account of the habits of the gypsy and brown-tail moths 

 and the methods used in their control may help in explaining the 

 purposes and possibilities of moth thinnings. The present means 

 of righting the moths may be classified under three heads, direct 

 entomological methods, indirect entomological methods and forestry 

 methods. The direct entomological methods seek the destruction 

 of the moths in one of their various forms by human agency, as in 

 spraying or creosoting. The indirect methods seek the propagation 

 of parasites or disease which will destroy the moths. The forestry 

 methods seek the eradication of tree growth which is favorable to 

 the moths, and, conversely, the encouragement of growth unfav- 

 orable to their development. 



It has been found, from our own and from European observations 

 and experiments, that although it will eat practical!} 7 all kinds of 

 vegetation, the gypsy moth thrives only on a limited number of 

 species of trees. These trees, which are the oaks (especially the 

 white oak), willow, cherry and fruit trees, and probably the gray 

 birch, may be called " non-resistant " trees. The brown-tail moth 

 is virtually the same, except that it will not eat coniferous growth 

 (pines, etc.) at all. Unless a large proportion of their food con- 

 sists of the leaves of these "non-resistant" trees, under ordinary 

 conditions both gypsies and brown-tails will soon either pass on to 

 a more favorable feeding ground or die. Therefore forestry methods 

 rather than attempting to destroy the moths themselves would de- 

 stroy their food. If we grow forests of resistant species, as conifers, 

 maple, ash, chestnut, etc., the moths will cease to be destructive. 



