76 ENTOMOLOGICAL SOCIETY OF ONTARIO. 



Mr. Smith, in discussing this paper, said that he thought the experiment entered 

 tipon in West Virginia well conceived, but thought that parasites did not greatly benefit 

 the farmer. Mr. Hopkins, in reply, slated that it required enormous numbers of the 

 Scolytids to kill the pine trees, and that his idea was to get some means of reducing the 

 numbers of the beetles and not completely exterminate them. That parasites were a 

 benefit to agriculture was, he thought, demonstrated by the irruptions of pests which took 

 place when, by some means, they reached localities from which their parasite was absent. 



PARASITIC AND PREDACEOUS INSECTS IN APPLIED ENTOMOLOGY. 

 By C. V. Riley, Washington, D. C. 



The importance to man, and especially to the agriculturist, of the parasitic and pre- 

 daceous insect enemies of such species as injure vegetation, has been recognized by almost 

 all writers on economic entomology. Indeed, it is a question whether the earlier writers 

 did not attach too much importance to them ; because, while in the abstract they are all 

 essential to keep the [)lant-feeding species in proper check, and without them these last 

 would unquestionably be far more difficult to manage, yet, in the long run, our worst in- 

 sect enemies are not materially affected by them, and the cases where we can artificially 

 encourage the multiplication of the beneficial species are relatively few. While fully 

 appreciating the importance of the subject, therefore, it is my purpose in this paper to 

 point out the dangers and disadvantages resulting from false and exaggerated notions 

 upon it. 



There are but two methods by which these insect friends of the farmer can be effectu- 

 ally utilized or encouraged, as, for the most part, they perform their work unseen and 

 unheeded by him, and ai-e practically beyond his control. These methods consist in the 

 intelligent protection of those species which already exist in a given locality, and in the 

 introduction of desirable species which do not already exist there. 



The first method offers comparatively few opportunities where the husbandman can 

 accomplish much to his advantage. That a knowledge of the characteristics of these 

 natural enemies may, in some instances, be easily given to him, and will, in such in- 

 stances, prove of material value, will hardly be denied. The oft quoted experience which 

 Dr. Asa Fitch recorded of the man who complained that his rosebushes were more seri- 

 ously afiected with aphides than those of his neighbors, notwithstanding he conscientiously 

 cleaned off all the old parent bugs (he having mistaken the beneficial ladybirds for the 

 parent aphides) may be mentioned in this connection. Other cases will recur to you, and 

 I will mention one rather striking experience related by my assistant, Mr. L. 0. Howard. 

 The Army Worm [Leucania unipuncta) was overrunning a large and valuable field of 

 timothy and threatened the destruction of the adjoining fields. The in.sect was as yet, 

 however, circumscribed and susceptible of remedial treatment. The owner of the field, 

 observing the buzzing swarms of the Red-tailed Tachina-fly, assumed that the fly was the 

 parent of the worms, and as the former was an active winged creature, capable of ex- 

 tended flight, he concluded that remedial work was useless, since the flies could, and 

 doubtless would, deposit their eggs over the entire surrounding country. As a conse- 

 quence the worm was allowed to travel to the adjoining fields and the injury thus in- 

 creased through ignorance of the fact that the Tachina flies were the most important of the 

 parasitic enemies of the worm. For many years well-informed gardeners in parts of 

 Europe have practised collecting ladybirds and some of the ground beetles to liberate 

 upon plants infested by plant-lice or by cutworms. The characteristics of these two 

 families, Ooccinellidif, and Carabidse, should be taught in our schools, as a definite know- 

 ledge of certain species, which is readily acquired, may often be turned to account in a 

 limited way by the cultivator. 



In a tew cases like this there is no reason why the farmer should not be taught with 

 advantage to discriminate between his friends and his foes, and to encourage the multi- 

 plication of the former ; but for the most part the nicer discriminations as to the bene- 



