20 



with the Red Scale (Aspidiotus aurantii Mask ell), although these were not so numer- 

 ous as they were at the time that I had them sprayed a little over one year previously. 

 The oranges when gathered in the following spring were quite free from the scales, 

 none of them having been rejected by the purchaser on account of being too badly 

 infested with these pests. Those who depend upon spraying for ridding their trees 

 of these scales usually spray their trees twice a year, in March or April, and again 

 in August or September, although some growers perform these operations only in the 

 autumn, the second spraying being given to the trees about two months after the 

 first. 



During the past season I have received numerous favors from you, especially in 

 the matter of identifying insects, for all of which please accept thanks. 

 Respectfully yours, 



D. W. Coquillett. 



Prof. C. V. Riley, 



United States Entomologist. 



THE GAS TREATMENT FOR THE RED SCALE. 



The process of treating trees with hydrocyanic acid gas for the de- 

 struction of scale insects (Family Coccidse) is now being extensively 

 used in southern California, not only in the orange groves, but also in 

 the nursery where the imported trees are subjected to this treatment 

 for the purpose of ridding them of insect pests. In Orange County 

 alone fully 20,000 orange and lemon trees have been subjected to this 

 treatment the present year in order to free them from the red scale 

 (Aonidia aurantii Maskell). 



Since the year 1887 various accounts of this process have been pub- 

 lished in some of the Annual Eeports and Periodical Bulletins of this 

 Department.* 



But as these are somewhat scattered, and include an account of the 

 various improvements that have been made from time to time, I have 

 thought it desirable to give in this place a brief account of this process 

 as at present used in actual field work, including in the account such 

 improvements as have been made since writing up my last report upon 

 this subject. Briefly speaking, this process consists in covering the 

 infested tree with an air-tight tent and afterward charging the tent 

 with hydrocyanic acid gas. The material commonly used in the con- 

 struction of the tent is what is known as blue or brown drilling. A 

 few persons have used common ducking in place of the drilling, but 

 this is much inferior to the latter; in the ducking the threads of which 

 it is composed extend only lengthwise and crosswise, whereas in the 

 drilling they also extend diagonally — this belonging to the class of 

 goods to which our merchants apply the term "twilled" — and for this 

 reason the drilling is both stronger and closer in texture than the 

 ducking. 



* See Annual Report United States Department of Agriculture for the year 1887, 

 pp. 123-142 ; and 1888, pp. 123-126. Also Insect Life, vol. 1, pp. 41,42 and 286 j and 

 vol. ii, p. 202-207. 



