238 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



larva? outing out irregular patches of the tissue in the leaves, leav- 

 ing only the upper and lower surfaces, the lower leaves being 

 infested the worst. The leaves are ren- 

 dered unfit for wrappers, splitt ng and 

 tearing very easily on account of these 

 blotches. A larva does not confine its 

 work to one place, but makes several 

 mines, and a single larva may thus destroy 

 the value of a leaf for wrapping purposes. 

 This migratory habit is of considerable 

 importance, as in leaving the old and in 

 making new mines the larvae 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 (Solarium carolinense), which fact 

 further emphasizes the 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 simply 

 crushing them with the hand, and this can 

 be done quite rapidly, and if done before 

 the mines become numerous should be 

 sufficient to check the injury. Where 

 spraying with Paris green is practised 

 against the hornworm 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. 



FIG. 171. Work of 

 split-worm reduced. 

 (After Howard, U. S. 

 Dept. Agr.) 



