THE SWEET-POTATO LEAF-FOLDER. 11 



the mortality ranged from 93 to 95 per cent ; in plat No. 3 mortality 

 was a fraction higher, about 95 to 96 per cent. 



All the plats were sprayed with a hand sprayer holding about 5 

 gallons of spray mixture, and probably a little more thoroughly than 

 would be done on a large scale by inexperienced help. When potatoes 

 are planted on soils with high nitrogen content, the foliage is usually 

 heavy, requiring careful manipulation to secure thorough distribu- 

 tion of the spray mixture. 



SUMMARY OF SPRAYING EXPERIMENTS. 



The foregoing experiments demonstrate that the larva? of the sweet- 

 potato leaf -folder (Pilocrocis tripunctata Fab.) can be killed readily 

 by timely applications of arsenical sprays. Either arsenate of lead 

 or zinc arsenite at the rate of 1 or 2 pounds (powder) to 50 gallons 

 of water will give favorable results. If the spraying is done early, 

 one application may be sufficient, whereas if treatment is delayed 

 until a large number of larvae have spun cocoons, two or more appli- 

 cations may be necessary in order to effect complete control. 



SUMMARY. 



The caterpillar of a pyralid moth (Pilocrocis tripunctata Fab.) 

 was very injurious to the foliage of sweet potato in southern Texas 

 during the fall of 1916. No previous instance of injury appears to 

 be recorded although the insect has long been known to inhabit the 

 Gulf region. It occurs also in the West Indies and has been men- 

 tioned as feeding on the sweet potato in Porto Rico. 



The various stages of this insect, which, because of the habits of 

 the larva, has been given the name of " the sweet-potato leaf-folder," 

 have been described from life-history studies carried on at Baton 

 Rouge, La. 



The minimum length of time required for the life cycle in the 

 insectary at Baton Rouge, La., was found to be about 26 days. In 

 the field there are probably 4, and possibly 5, generations a year in 

 the latitude of Baton Rouge. The winter months apparently are 

 spent in the last larva stage within a cocoon at or near the surface 

 of the soil. 



Two parasitic flies have been reared from the larvae, and the spined 

 soldier-bug has been found to be predacious upon the larvae. In 

 Texas the " jackdaw " or boat-tailed grackle feeds upon them. 



Experiments conducted by the Bureau of Entomology indicate 

 that the larvae can be killed readily by spraying the foliage with 

 either arsenate of lead or arsenite of zinc at the rate of 1 or 2 pounds 

 (powder) to 50 gallons of water. 



