139 



good. This is particularly true of those of our Coccidae and Aphi. 

 didae and those of our Lepidopterous larva} which have numerous natu- 

 ral enemies of their own class; and it not only emphasizes the impor- 

 tance of preventive measures, which we are all agreed to urge for other- 

 cogent reasons, and which do not to the same extent destroy the para- 

 sites, but it affords another explanation of the reason why the fight with 

 insecticides must be kept up year after year, and has little cumulative 

 value. 



But the problem of the wise encouragement and employment of the 

 natural enemies of injurious insects in their own class is yet more com- 

 plicated. The general laws governing the interaction of organisms are 

 such that we can only in very exceptional cases derive benefit by 

 interference with them. The indigenous enemies of an indigenous phy- 

 tophagous species will, cceteris paribus, be better qualified to keep it 

 in check than some newly introduced competitor from a foreign coun- 

 try, and the peculiar circumstances must decide in each case the 

 advisability of the introduction. The multiplication of the foreigner 

 will too often involve the decrease of some indigene. If a certain phy- 

 tophage is generally disastrous in one section and innocuous in another 

 by virtue of some particular enemy it will be safe to transfer and 

 encourage such enemy, and this is particularly true when the phy- 

 tophage is a foreigner and has been brought over without the enemy 

 which subdues it in its native home. Icerya had some enemies in Cali- 

 fornia, presumably American, but they were not equal to the task 

 of subduing it. Yedalia, in the Icerya's native home, Australia, was 

 equal to the task and maintained the same superiority over all others 

 when brought to America. The genus was new to the country and 

 the species had exceptionally advantageous attributes. But there is 

 very little to be hoped from the miscellaneous introduction of preda- 

 ceous or parasitic insects for the suppression of a phytophage which 

 they do not suppress in their native home or in the country from which 

 they are brought. 



The results of the introduction by Mr. A. D. Hopkins of Clermformi- 

 carius to contend with the Scolytids which were ruining the West Vir- 

 ginia pines were doubtful, for the reason that indigenous species of the 

 genus were already at work in America. Yet the experiment was safe 

 and desirable, because the European Olerus is more active and more 

 seemingly effective than our indigenes. The Gypsy Moth was evidently 

 introduced into Massachusetts without its European natural enemies, 

 and as in some parts of Europe it is often locally checked by such natural 

 enemies, a great number of which are known, a proper study of them 

 and the introduction of the most effective could result in no possible 

 harm and might be productive of lasting good. Such a course was 

 advised by me at a conference upon the subject held in the rooms of 

 the State Board of Agriculture, Boston, March 4, 1891,* and in corre 



INSECT LIFE, in, p. 369, ff. 



