IXSEPTS TXJrRTOrS TO THE HOP-PLAXT. 



281 



hop-plants, where tliey are to be found. When the cater- 

 pillars of this brood are numerous they sometimes do con- 

 siderable damage to the foliage, but both this and the 

 following species are ordinarily prevented from becoming 



Fig. 162. — The Comma-butterfly {Polygonia comma), a, egg-chain, 

 h, larva; c, chrysalis; d, adult— all natural size, except a, which 

 is greatly enlarged. (After Howard, U. S. Dept. Agr.) 



overnumerous by several parasites of the eggs and larvge. 

 Only when for some reason conditions are unfavorable to 

 the development of its parasites does either S23ecies become 

 especially abundant. In fact. Dr. J. B. Smith, who made 

 extensive observations upon hop-insects in 1883, states 



