The Bulletin. 



29 



these weeds be kept down in the vicinity of the tobacco field, other- 

 wise they will furnish crop after crop of horn worms for the tobacco 

 field. 



Natural Enemies. — Living exposed upon their food plants as they 

 do, Horn Worms are subject to the attacks of a number of natural 

 enemies. Chief among these natural checks is a kind of bacterial 

 disease which causes the worms to turn black, shrivel up and die. 



Every tobacco farmer is aquainted with the work of the small four- 

 winged parasitic fly. This parasite lays its eggs upon the Horn 

 Worm and the larvae live in the interior of the Horn Worm until full 

 grown. When full grown they come to the surface, where they spin 

 white oval cocoons. Horn Worms covered with these cocoons are 

 frequently seen in tobacco fields. (Fig. 15.) Such worms should 



Fig. 15. — Larva of Southern Horn Worm with_cocoons of a para- 

 site, slightly reduced. 



(Photograph by the author.) 



not be destroyed, for their days for doing damage are practically 

 over, and the parasites issuing from them would mean the destruc- 

 tion of an increasing number of Horn Worms in the next generation. 

 Several kinds of two-winged flies have also been reported as 

 enemies of horn worms. 



Control. 



Preventives. — Fall and winter plowing, if deep, has a tendency 

 to expose the over-wintering pupse to the action of heat and cold, thus 

 killing a great many. All weeds should be kept down in the tobacco 

 field, especially such weeds as are naturally food plants for the Horn 

 Worm. 



