October, '13] REVIEWS 431 



The journej^ was made possible through the generosity of Mr. Carnegie. The au- 

 thor's itinerary included Washington and most of the Federal Field Stations as well 

 as a number of the more important (from an entomological standpoint) Agricultural 

 Experiment Stations, Entomological Departments of Universities and offices of 

 State Entomologists. The first part discusses organization and agencies, and the 

 second gives a summary of control methods as practised in this country. The critical 

 remarks upon the biological method of controlling insects are especially valuable 

 and a translation of these by Dr. E. A. Schwarz, transmitted through the courtesy 

 of Dr. Howard, follows: 



"We have now learned [in the preceding chapters] of a variety of biologic warfares. 

 The success of them was very diversified; excellent in some cases; in others less 

 satisfactory, and, again, in others entirely negative. From this fact it is to be 

 concluded: (1) It is not an Utopia [a dream] but an established fad that insect calam- 

 ities can be successfully fought and terminated by artificial rmdtiplication or importation 

 of parasites; (2) but on the other hand we learn therefrom ■ that the biologic method does 

 not constitute an universal remedy. 



"It is self evident that a warfare by means of parasites can only be successful 

 where the devastation is due to a scarcity or absence of parasites. There is a whole 

 series of insect eruptions which are caused by other factors: for instance, the multi- 

 plication of Scolytid beetles depends much less upon the diminution of the number 

 of parasites and enemies than on the increase of food material. In this case it would 

 be of no use to introduce Clerus formicarius and the various Ichneumonids if at 

 the same time care had not been taken to remove the dying trees. Or, take the 

 case of the Phylloxera which in the vineyards of Europe does such tremendous 

 damage. It would be a useless attempt to counteract this pest with natural enemies. 

 For it is not the absence of such enemies which renders the Phylloxera such a dreadful 

 pest in Europe, but the real cause is the smaller power of resistance of the grape 

 vines. M-any similar instances could be given. 



"But apart from s ich cases where the biologic method necessarily appears to 

 be excluded, there are still other cases where in spite of apparent possibility the 

 biologic warfare is not employed and the mechanical warfare is preferred, namely 

 in cases where we have to deal with a very short outbreak and where we have imme- 

 diately to use remedies; or in cases where we have on hand cheap, easily applicable 

 and sure, mechanically acting remedies. For we must not lose sight of the fact 

 that parasites and enemies are also subject to all sorts of influences by which their 

 efficacy is again lowered or delayed so that the degree of the efficiency [of the biologic 

 method] can not be foretold with the same degree of certainty as with many technical 

 methods. 



"Finally there are cases where the biologic method is to be used only to assist 

 the mechanical method. For instance, where the caterpillars are, by the lime rings, 

 prevented from ascending the trees, the efficacy of this mechanical remedy can be 

 essentially increased by the protection and introduction of parasites, etc. 



"That the Americans are fully and correctly aware today of all these points, is 

 made sufficiently clear from the foregoing report [i. e. in the body of the book]. To 

 be sure, there was a time when too optimistic views were indulged in by some, and 

 when the biologic warfare was considered as an almost universal remedy, — namely 

 at the time when the importation of Nanus cardinalis resulted in such a wonderful 

 success. But those times are gone. At least the leading entomologists of America, 

 with Howard in their lead, never think of fighting all pests with parasites; they 

 are too well aware that this method is only adapted to certain specific cases. And 

 fmlher, they have also learned in the meantime that the introduction and accli- 

 matization of parasites is not always such an easy matter as in the case of Novius 



