20 BULLETIN" 416^ V. S. DEPAKTMEJS^T OF AGEICULTUKE. 



In the course of many field examinations we have often seen 

 predatory uisects which had been entangled in the red spider's web- 

 bing and had perished. TrijMeps insidiosus and other species have 

 been frequently caught in this manner. As Quayle (1912) has 

 recorded, Arthrocnodax appears very much at home among the fibrils 

 of the mite web and probably derives some protection from the chal- 

 cidid AjDhanogmus. 



Clustering before rain. — Immediately before heavy rains mites are 

 often seen clustered in groups. This was never seen at any other time 

 than just prior to the first drops of a heavy rain. 



NATURE AND EXTENT OF DAMAGE TO COTTON IN THE SOUTH. 



The detailed accoimt of the specific feeding method and immedi- 

 ate injury inflicted by the red spider we have already presented. It 

 has been shown that severe infestation causes such a lessened vital- 

 ity, and possibly toxic condition, that a shedding of the leaves and 

 bolls is induced. In severe cases the death of the stalk usually follows 

 the complete defoliation of the plant. However, the loss of foli- 

 age (PI. V, figs. 1-3) is always accompanied by the shedding of the 

 bolls, which may amount to the total elimination of the fruit or to 

 the loss merely of the younger boUs. In the case of stalks which 

 have suffered the complete loss of foliage but which have retained 

 certain of the oldest bolls, the latter may open and produce lint, if 

 sufficiently mature. These defoliated plants are rarely productive 

 of any considerable amount of cotton, though in some cases they 

 develop considerable adventitious foliage and may become restored 

 abnost to normal appearance. 



The damage worked by red spiders in cotton fields varies in intensity 

 and extent according to the nature of the dispersion centers, and de- 

 pends on whether control measures have been applied and upon other 

 factors. In 97 cases brought to our attention during one season (1912) 

 the average infested area for each case was 21 acres. In other words, 

 ^ a total of about 2,037 infested acres of cotton was voluntarily reported 

 from South Carolina during one season. It is a conservative estimate 

 to presume that this does not represent over 10 per cent of the total 

 affected acreage in the State for that year. This would make the 

 infested area in South Carolina about 20,370 acres, which would 

 normally produce a crop of about 13,580 bales or 6, 790,000 pounds. 

 The proportionate part of this output that might be expected to be 

 lost through the ravages of the red spider is about two-fifths, or 

 2,716,000 pounds. At 12 cents per pound for the staple, this lost lint 

 wiQ represent a tax of $325,920 to the State, and the value of seed 

 correspondingly lost would ordinarily amount to $67,900. Our figures 

 thus indicate that during the season of 1912 the red spider caused a 

 loss of about $393,820 to the cotton planters of the State of South 



