228 



INSECTS iKJURlOrs TO STAPLE CROPS. 



making new mines the larvse must necessarily eat a certain 

 amount of the surface of the leaf, and can thus be killed 

 by an arsenical spray. The life-history of the insect is 

 not completely known, but as only about twenty days are 

 required for all its transformations, several broods probably 

 occur during a season. The original food-plant of this 

 pest has been found to be the common horse- or bull-nettle 

 (Solamim carolinense), which fact further emi^hasizes the 



Fig, 127. — Tobacco Split- worm. Adult moth above; larva below at 

 right; pupa below at left, with side view of enlarged anal seg- 

 ment — all enlarged. (After Howard, U. S. Dept. Agr.) 



caution already given, to keep all weeds carefully cut down 

 around the tobacco-field, especially those nearly related to 

 tobacco botanically. Many planters destroy the larvae by 

 simj)ly crushing them with the hand, and this can be done 

 quite rapidly, and if done before the mines become numer- 

 ous should be sufficient to check the injury. Where 

 spraying with Paris green is practiced against the Horn- 

 worm it should be sufficient to destroy most of the miners, 

 as, if the leaf is thoroughly coated with poison, they would 

 get a fatal dose in starting a new mine. 



