PROGRESS REGARDING SUGAR-BEET WEB WORM. 59 



LIFE HISTORY AND HABITS. 



In rearing experiments conducted at Rocky Ford, Colo., the average 

 time required from the deposition of the eggs until the moths issued 

 was a little more than a month. The egg stage was observed to vary 

 from 3 to 5 days, the larva stage from 17 to 20 days, and the pupa 

 stage was usually 11 days. These variations were from records of 

 successive generations. 



So far as the writer has been able to determine, there are three 

 generations or " crops " of webworms in the Arkansas Valley each 

 year. There may be a fourth generation, but if so it is not clearly 

 marked and possibly occurs early in the season on weeds such as 

 Russian thistle (Salsola tragus) and lamb's-quarters (Cheno podium 

 album ) . For the sake of convenience we may assume that only three 

 generations occur yearly. The periods during which the writer ob- 

 served the w T ebworms of these successive generations in evidence on 

 sugar beets in the Arkansas Valley ranged from about the middle 

 of June until early July for the first generation and from about the 

 middle of July until well into August for the second generation, 

 while the third brood occurred in September. 



In reality the generations are not sharply marked and considerable 

 overlapping may occur. In general the danger period extends from 

 shortly before the middle of June until well into September. The 

 first generation of webworms may be expected at its height of destruc- 

 tiveness during the latter half of June, at a time when the beets are 

 comparatively small and least able to resist the attack. (See fig. 

 14.) At this season the infested beets may actually be killed by this 

 webworm, which, after eating all the leaves, may destroy the crown 

 of the plant. Whenever the crown is destroyed the beet dies. So 

 far as the writer has observed, the acreage destroyed in this way is 

 very small and ordinarily occurs only when the infested beets are 

 young and the available leaf surface limited. By the time the 

 " worms " of the later generation are present the beets have become 

 of good size and, although they may be completely stripped of all 

 but the youngest leaves, it is rarely that any are killed. (See fi>s. 

 11, 12.) " 



The larvae of the first generation, after maturing and burrowing 

 into the ground, pupate promptly and the moths issue within a few 

 days and deposit eggs for the second generation. The " worms " of 

 this next generation, on reaching maturity, likewise burrow into the 

 ground and spin their tubelike cases. However, only about half of 

 them pupate promptly, the others remaining unchanged in the tubes 

 until the spring of the following year. From the pupae which develop 

 in August, moths issue which deposit eggs for the third or September 

 generation, and these " worms " remain unchanged throughout the 



