72 INSECTS AND HUMAN WELFARE 



cally inhibit the development of undergrowth on the forest 

 floor) with mixed forests of deciduous trees, that we may have 

 overlooked some fundamental principle regulating insect 

 damage to trees of the two types. That such is not the case 

 is shown by the less noticeable, and more restricted out- 

 breaks of certain species that occur in deciduous forests where 

 one species of tree may greatly predominate, or in cases of 

 insects that readily attack a considerably extensive series of 

 trees. That the excessive importance of forest insects in our 

 own country may in part b^' due also to the great amount of 

 waste, uncared-for land suggests another factor which may 

 perhaps modify these conclusions. 



The striped maple caterpillar {Anisota rubicunda) is an 

 example of the first type mentioned above. This is a defoliat- 

 ing species, of rather general distribution in the cooler por- 

 tions of eastern North America. It is naturally always more 

 abundant where maples are numerous, but occasionally 

 appears in localized outbreaks of quite definite duration. 

 An example of the other type is the European gipsy moth 

 {Porthetria dispar. Fig. 33), now prevalent in a part of New 

 England where it became established as a result of accidental 

 introduction, through the agency of man. 



The gipsy moth lives as a caterpillar on the foliage of a 

 large number of deciduous trees, and will, when pressed for 

 food, devour with evident relish many shrubs. Even the 

 foliage of pines and other conifers will serve as food for the 

 caterpillars after they have become partly grown. Although 

 certain trees such as the oaks are its favorite food it is a truly 

 polyphagous insect and a forest of deciduous trees contains 

 few species which it will not readily attack. It finds com- 

 monly, therefore, conditions very similar to those en- 

 countered by the enemies of coniferous trees. Consequently, 

 we find that its history in Europe, as far back as it has been 

 recorded with accuracy, includes a series of sudden outbreaks. 

 Thus in Europe in 1731, 1761, 1794, 1837, 1871, and 1909, 

 certain localities were visited by hordes of these caterpillars 

 which defoliated everything in the vicinity. It is very re- 



