65 



Generally speaking, successive periods of extraordinary abun- 

 dance of a species in any locality or district show little correspondence 

 to any possible life cycle, being too various and irregular for that 

 interpretation. Extensive parasitism of imagos and larvae by insects, 

 annelids, Protozoa, and fungi produces widespread and destructive 

 epidemic diseases, a knowledge of whose prevalence and status is es- 

 sential to any safe prediction of periods of destructive abundance of 

 the white-grubs. 



The May-beetle species known as Phyllophaga fusca and P. futilis 

 were evidently those which produced most of the white-grubs which 

 were so abundant in northern Illinois in 1912 as to do heavy damage 

 to farm crops in several counties. Two thirds of the collections made 

 in that section in 1914 were of these species, the first of the two 

 mentioned being, however, nearly four times as abundant as the 

 second. ~~ ^ 



The facts concerning the food-plants of the more abundant species 

 are grouped and classified in a way to distinguish trees and shrubs 

 especially attractive to them, and consequently dangerous to adjacent 

 crops by reason of the abundance of white-grubs to descend from them. 



