40 STORRS AGRICULTURAL EXPERIMENT STATION 
tial explanation of this fact is found in the many disturbances 
of nature, chief among which is the removing of our forests, 
which has forced insects to change their diet. It is true that 
many species have been imported and others have been more 
thoroughly distributed. We now have a much better knowl- 
edge of insects and consequently they come more frequently 
under our observation. The question is also largely one of 
ideals. Our ancestors were satisfied with smaller yields and 
lower quality; that is, they did not seek for that perfection 
with which our modern growers are so much concerned. 
NATURAL ENEMIES. 
The great controlling factor in the insect world is the pres- 
ence of certain species of insects that prey upon others of 
their kind. It is probable that climatic conditions have their 
influence, but the fact that the Apple Leaf-Miner has not be- , 
fore appeared in injurious numbers we believe to be largely 
due to the efficient work of certain insect parasites. Brunn 
found two species of Chalcid flies (Sympiezus lithocolletidis 
Howard and Astichus tischeria Howard) preying on this in- 
sect. Twoother species, which were identified by Dr. Ashmead 
as Closterocerus tricinctus Ashm. and Systomspiesis nigrife- 
morata Ashm, were found in vast numbers during the past 
season busily engaged in depositing eggs on the surface of 
the mines. Later in the season the pupae of these flies were 
found to have appropriated the comfortable quarters of the 
miners which had been killed (Fig. 4). 
? 

Fic. 4—Two pupa of parasitic flies beside their dead victim 
(About twice natural size). 
