202 



Curtice's material and can corroborate the correctness of the determi- 

 nation. In this connection we also draw attention to the interesting 

 communication of Dr. Elizabeth R. Kane (p. 238) relating to the travel- 

 ing propensities of the young Hypoderma larva. 



THE USE OF HYDROCYANIC ACID GAS FOR THE DESTRUCTION OF 



THE RED SCALE. 



By D. W. Coquillett, Los Angeles, Cal. 



In my reports to Professor Riley for the years 1887 and 1888, pub- 

 lished in the annual reports of this Department for these years (pages 

 123 to 142, and 123 to 126 respectively), I gave an extended account of 

 the use of hydrocyanic acid gas for the destruction of scale-insects (family 

 Coccidw) ; and I am not aware that anything has been published upon 

 this subject since the appearance of the above-mentioned report for the 

 year 1888. On page 126 of this report I gave an account of treating 

 several orange and lemon trees with this gas, and the latest report 

 given of the condition of these trees was under date of August 15, 1888 ; 

 under date of February 17, 1889, the owner of the trees, Mr. I. L. Col- 

 lins, wrote me as follows in regard to them : 



Dear Sir: I received yours of the 15th inst. asking about the condition of the 

 lemon and orange trees treated with the gas. These trees are in a much better con- 

 dition than those around them, as they have a full foliage while the others are nearly 

 bare; what fruit they have on is comparatively clean, there being but few red scales 

 on them. They already show that the coming season they will bear quite heavily, 

 but now they have enough red scales on them to ruin them in a year. We expected 

 that the scales would come on them agaiu from the other trees, these not having been 

 treated with the gas ; I did not think the tops worth saving, so did not treat them 

 with the gas. I will cut off the tops, as almost everybody else is doing, and will wash 

 the stumps with a solution composed of 30 pounds of resin, 7 pounds of caustic soda 

 or potash, and one gallon of fish oil to 100 gallons of water. The trees treated with 

 the gas remained perfectly clean for over a month ; then we found scales on the out- 

 aide branches, having apparently been carried there by the horses in cultivating. 



In accordance with a written request from several of the orange 

 growers of Orange, I went down to that place in the latter part of Sep- 

 tember of the present year, and conducted a series of experiments with 

 hydrocyanic acid gas for destroying the Red Scale, with the view of try- 

 ing to discover some simpler and less expensive method for producing 

 and manipulating this gas than the oue heretofore in use. The lemon 

 trees experimented upon and also the fumigating outfit used in making 

 these tests were kindly placed at my disposal by their owner, Mr. A. 

 D. Bishop ; and the latter gentleman, in conjunction with Mr. A. H. 

 A 1 ward, also aided me in moving the outfit from tree to tree when mak- 

 ing the tests. Among the different methods tried was one that gave 

 very satisfactory results, and which, both iu regard to expense and 

 labor, is a great improvement upon any heretofore tried. It consists 



