A NATIONAL PLAN FOR AMERICAN FORESTRY 731 



beetles. In the case of materials used in rustic construction, cutting 

 at certain seasons of the year or treating with repellent sprays affords 

 ample protection. Such information has been disseminated through 

 letters and bulletins and personal contacts to such an extent that many 

 mills and operators are fully aware of the possibilities of insect losses 

 and many are adequately guarding against it. 



BENEFICIAL FOREST INSECTS 



All forest insects are not destructive. There are many species of 

 beneficial insects known as predators or parasites the former devour 

 the host bodily, the latter usually feed within the body of the host. 

 Occasionally these predators or parasites are the controlling factor in 

 the decline of an outbreak of forest insects. A great deal has been 

 learned about the handling and practical use of certain forms of these 

 beneficial insects, particularly those preying on the gipsy moth. 

 The predators and parasites of this species were introduced from 

 Europe and Japan and established in this country with marked con- 

 trolling effect on this destructive pest. The pine tip moth was 

 accidentally introduced into the pine plantations of the Nebraska 

 National Forest and for a number of years so retarded the growth of 

 these trees that the abandonment of the use of pines as planting stock 

 was seriously considered. In 1925 a few parasites of this tip moth 

 were collected in Virginia and liberated at Halsey, Nebr. These took 

 hold with remarkable rapidity, and by 1930 had destroyed practically 

 90 percent of their hosts, effecting satisfactory control of the tip moth. 

 For the past 2 years the effect of this control has been clearly shown 

 in the increased vigor and height growth of the trees. At the present 

 time parasites of several destructive foreign pests such as the larch 

 sawfly, the European pine-shoot moth, and the birch sawfly are being 

 studied in Europe, with the idea of eventually controlling these pests 

 in this country through the establishment of their enemies. There 

 are great possibilities in this field which have hardly been touched. 



INSECTS AND FUNGI 



The interrelation of insects and fungi presents many interesting 

 technical problems, the solution of which may have a very practical 

 bearing on insect control. For several years the entomologists and 

 pathologists have been cooperating in this field. It has been demon- 

 strated that some of the most destructive species of bark beetles 

 introduce fungi so-called "blue stains" into the tree when they 

 attack it, and that these fungi play an important role in hastening the 

 death of the tree and possibly in furnishing conditions necessary for 

 the development of the beetle broods. In at least one case this blue 

 stain alone is capable of killing the tree. It is not going too far to 

 say that a more complete knowledge of the intricate relationships of 

 insects, fungi, and the tree may lead to an entirely different conception 

 of this whole problem and to better control much as the determina- 

 tion of the interrelation of the mosquito and malaria parasite led to 

 modern prophylactic methods in the control of malaria. There are 

 many such complex interrelations between fungi and insects. For 

 example, the sporadic dying of oaks in the southern Appalachians 

 presents a complex of insects and diseases which we know little about 



