INJURIOUS IP^SECTS. 



G. II. Perkins, Ph. D. 



I'rofossor or Natural Jlistoi'^' in the Uiiiver.sity ot Vciniont. Eiilouiologifct to tl 

 State Afjrrifiiltural Kxi)eriiuent Station. 



METHODS OF PREVENTING OR CIIECKL\(, THE 



ATTACKS OF INJURIOUS INSECTS.— 1. INSECT 



ENEMIES OF INJURIOUS INSECTS. 



Ill order that we may meet the attacks of destructive insects 

 with any chance of success, it is necessary, iirst, that we understand 

 something of the structure, liabits, and mode of development of 

 each species ; and, second, that we be able to devise some method 

 by which the enemy may be driven ofi, or, if possible, exterminated. 

 Usually the war must be one of extermination, for, as every farmer 

 7m«L,only too well knows, insects when driven oft' very often return 

 speedily, and with re-entorcement. Thus the study of insects^/of 

 insecticides must be carried on together. New insects are every now 

 and then appearing, some of them injurious, some beneficial, some 

 neither. Most injurious insects are attacked in one way or another 

 by other insects. These may be either parasitic upon eggs, larva, 

 pupa or imago, that is, upon anv of the difterent stages which 

 ordinarily occur in the life of insects, and sometimes an injinious 

 insect is attacked in each of these stages by a difterent enemy. 

 The sudden decrease in the niiml)er of insects, which every one 

 has now and then observed, is often due to the destruction caused 

 by parasitic insects. I remember a season some years ago, when 

 canker worms were most ruinously abundant, so much so, that 

 the citizens of the infested town were quite in despair eoncerning 

 elms and other trees, and the ))rospects for the next season were 

 certainly discouraginof ; but, to the agreeable surprise of everv one, 

 the next season brought not only no increase of the canker worm, 

 but so very marked a decrease as to well-nigh render cftbrts for 

 the prevention of further damage to the trees unnecessar\', and, 

 tor a number of years after this, there was no return of the 

 pest. This deliverance was due to the attacks of certain parasites, 

 which so eftectually destroyed the canker worms as to nearly dii\e 



