. THE RED SPIDER ON COTTON. 25 
sible to the mites which may be crawling about in search of green 
plants, and, likewise, the basal leaves favor greatly the reestablish- 
ment of red spiders which may become stranded while being carried 
in surface water. 
Appearance of spring adults —The date which marks the maturity 
of the progeny of the females which wintered through from the pre- 
ceding fall is subject to some variation. In 1911 the first spring 
brood was maturing as early as March 11, while in 1912 the first 
females did not appear until about April 17. In both 1913 and 1914 
this brood matured about March 25. 
Time of violet devastation.—Usually fobvand the end of May the 
cultivated violet plants in the Southeast become so completely over- 
run with red spiders that they are killed to the ground. The first 
indication of damage to violets is the presence of russet spots on the 
leaves. As the infestation increases the appearance of violet borders 
is as though they had been fire swept. Those who see them invari- 
ably believe they have been killed by drought. (Pl. IV, fig. 4.) 
When violets grow within a few hundred feet of cotton they may 
constitute the immediate source of infestation. 
The average date of maximum injury to cultivated violets, as shown 
by the observations of the last four years, is found to be May 25. This 
is important in the seasonal history of the red spider, since the death 
of so many violet plants precipitates the migration of the mites, with 
the result that the pest becomes established on many new hosts. 
Time of establishment on cotton.—The earliest date for the estab- 
lishment of the red spider on cotton varies somewhat from season to 
season. The time depends largely on the date of appearance of the 
crops, since we frequently find females established on seedlings which 
are only three or four days old. Mites have occasionally been seen 
established on cotton as early as the 1st of May, but for the seasons 
1911, 1912, 1913, and 1914 the average for the first records on cotton 
is computed to be May 20. The lower (sandy) section of South 
Carolina averages one-half month earlier in the pest’s appearance 
than does the upper (clay) section, June 25 marking the time of the 
beginning of damage for the former and July 10 for the latter. 
Time of severest wnfestation.—The progress of infestation in a given 
field depends on several interrelated factors, such as temperature, 
precipitation, natural enemies, etc. Furthermore, there are succes- 
sive waves of infestation occasioned by the favorable and the inimical 
natural agencies. In 1911, at Batesburg, a cotton field was seen 
very acutely infested on June 12, while in 1913 fields were seen badly 
infested as late as September 6. Most of the severe infestation, how- 
ever, occurs during July and August. By averaging the dates of oc- 
currence of a considerable number of acute cases in our files we obtain 
July 26 as the date of heaviest infestation. 
n4380°—Bull. 416—17-—_4 
