Sugar Beet Webworm 



The worms which pupate in the fall become moths in about ten or 

 twelve days. After breaking out of the silken cocoons these moths mate 

 and the females lay eggs for a third brood. When full grown, the worms 

 of this brood enter the ground, where they remain in their cocoons, as 

 worms, until spring. 



How wisely Nature has provided for the carrying of the beet web- 

 worm over the winter! For fear that an early winter overtake the last 

 brood in the fall and they perish, a part of the second brood is set aside 

 as a sort of sinking fund against such a calamity. There is a considerable 

 overlapping of the broods, so that the eggs and several sizes of worms may 

 be present at one time. 



NATURAL ENEMIES 

 Ichneumon -flies 



The dusky winged parasite 9 (Fig. 7, Plate V, Page 19) is one of the 

 most common enemies of the sugar beet webworm. The larva of this 

 parasite develops within the webworm, but does not kill it until after it 

 has entered the ground and spun its cocoon. Then instead of the moth, 

 the parasite emerges from the cocoon. 



This parasite has four dusky wings. Near the center of each of the 

 forward pair is a partially clear area. The body is dark reddish or bay 

 and the legs have dark bands which give them the appearance of being 

 ringed. 

 Braconids 



The little wasp-like parasite 3 (Fig. 14, Plate V, Page 19), which is a 

 Braconid, frequently emerges from a cocoon instead of the webworm 

 moth. 



Tachina-flies 



The Tachina-fly 16 (Fig. 13, Plate V, Page 19) fastens its eggs onto 

 the webworm and when the maggots hatch they burrow into it. At first 

 the webworm appears to be little disturbed by the maggots, but as the 

 latter increase in size their feeding weakens the worm, which finally dies. 

 When fully grown, the maggots change to pupae inside the puparium 

 (Fig. 12, Plate V, Page 19). The adult fly breaks open the end of the 

 puparium, as shown in the figure, and escapes. 



Solitary Wasp 



One of the enemies of the sugar beet webworm belongs to a group of 

 wasps known as solitary wasps. (See page 135.) 



This wasp 13 (Fig. 15, Plate VI, Page 21) places its eggs in 

 tunnels, one of which is shown in cross section in Figure 14, Page 78. 

 These tunnels are dug in the soil about the borders of fields. 



The mouth of the tunnel is always built up a half inch or so above the 

 surface of the soil. When the nest is completed several web worms are 

 caught and after being stung, which paralyzes them, they are placed at 

 the bottom of the tunnel. After a single egg is deposited among the 

 worms a wall is built so as to make a small cell at the lower end of the 

 tunnel. The chimney-like mouth is next filled with mud. The larva 

 which hatches from the egg feeds upon the webworms until ready to 

 change to the pupa. This change takes place in the burrow, from which 

 the adult wasp escapes by digging its way out. 



(j-_u-i^ See explanation f "Reference Figures." page 2 



77 



