32 THE REPORT OF THE No. 33 



no other checks on their increase available. Frequently thousands of specimens 

 of a single species of leaf-defoliating insects may be taken at a single light trap, 

 in spite of the fact that no appreciable injury to its favoured food plants is 

 noted throughout the year. 



The answer is that natural enemies hold these species in adjustment so that 

 none but the expert fully realizes their presence. Because no serious damage 

 is done, there is little demand or opportunity to study the battle for survival 

 that is continually being waged by these contending forces. 



Because of insufficient study of these problems, which must of necessity 

 be carried on for a series of years, it is difficult to speak with assurance of the 

 value of any particular natural enemy. 



Again my remarks will be directed to the gipsy moth investigation. 



From 1869, when the insect first became established in North America, 

 until 1889, when it became so destructive that its identity became known, there 

 was a relatively slow increase, and all the native natural factors that might 

 function in its control were operative. During the next ten years the State of 

 Massachusetts made an attempt to exterminate the insect, which was found to 

 occur in an area of about 200 square miles. This work resulted in an enormous 

 decrease of the species, and when the work was discontinued by the state, not 

 only was it impossible to find defoliated trees in the infested area but the egg 

 clusters and caterpillars were so scarce that the public deemed the expense 

 unnecessary. In fact a special committee of the Massachusetts Legislature 

 reported, after numerous hearings, that the insect need not be considered a 

 serious pest and that "we find no substantial proof that garden crops or wood- 

 lands have suffered serious or lasting injury or are likely, with that precaution 

 or oversight which prudent owners are disposed to give their own interests, to 

 be subjected to that devastation which one would have the right to anticipate 

 from these reports. It appears to us that the fears of the farmers throughout 

 the State have been unnecessarily and unwarrantably aroused, evidently for the 

 purpose of securing the effect of those fears upon the matter of annual appro- 

 priations. . . . We do not share these exaggerated fears and the prophecies 

 of the devastation and ruin are unwarranted and in the most charitable view 

 are but the fallacies of honest enthusiasts." 



During this period a small force of experts made careful studies, both in 

 the field and in the laboratory, to determine the value of natural enemies and 

 the part they were playing in gipsy moth control. The results were not promis- 

 ing. A number of birds that feed on hairy caterpillars were found to attack 

 the gipsy moth, and toads and skunks were occasionally reported as feeding on 

 the species. A few native parasitic and predaceous enemies were noted, but 

 their abundance and the frequency of their attack gave little promise of relief. 



The wilt disease must have occurred in the field during this period, but the 

 records of its presence are very meagre. At any rate it was not abundant 

 enough to attract the notice of experts or give promise of decreasing the severity 

 of bad infestations. 



No attempt was made to introduce the natural enemies of the gipsy moth 

 from Europe during the years when extermination was being attempted, as it 

 was believed that the chances of control by parasites would be negligible when 

 exterminative work was under way. 



In the five years following the discontinuance of the work (1900 to 1905) 

 the insect increased and spread enormously and experience showed that it could 

 not only defoliate and kill trees, but that it was a veritable scourge to the people 

 in the region that was heavily infested. 





