[Reprinted from tin- Proceedings of the 5th Annual Meeting of the Association of 

 Economic Entomologists, held in Madison, Wis., August 15, 1893, and published 

 in Insect Life, Vol. vi, No. 2.] 



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 predaceous insect enemies of such species as injure veg- 

 etation, has been recognized by almost all writers on economic ento- 

 mology. 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 plant-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 insect enemies are not mate- 

 rially 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 pur- 

 pose in this paper to point out the dangers and disadvantages result- 

 ing from false and exaggerated notions upon it. 



There are but two methods by which these insect friends of the 

 farmer can be effectually utilized or encouraged, as, for the most part, 

 they perform their work unseen and unheeded by him, and are practi- 

 cally beyond his control. These methods consist in the intelligent pro- 

 tection 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 instances, 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 seriously affected 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 assist- 

 ant, Mr. L." O. Howard. The Army Worm (Leucania unipuncta) was 

 overrunning a large and valuable field of timothy and threatened the 

 destruction of the adjoining fields. The insect was as yet, however, 

 circumscribed, and susceptible of remedial treatment. The owner of 

 the field, observing the buzzing swarms of the Ked-tailed Tachina-fiy, 

 assumed that the fly was the parent of the worms, and as the former 



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