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WoGLUM (R. 6). Recent Results in the Fumigation of Citrus Trees 

 with Liquid Hydrocyanic Acid. — Jl. Econ. Entom., Concord, N.H., 

 xii, no. 1, February 1919, pp. 117-123, 2 figs. 



Hydrocyanic acid gas has been used for the fumigation of citrus 

 trees in California for more than thirty years and during this time 

 many changes have been made in the apparatus and methods adopted. 

 These are briefly reviewed, and are followed by a discussion of the 

 latest practice, in which liquid hydrocyanic acid is injected by means 

 of a fumigating machine at the edge of the tent as a mist, which 

 on evaporating is left with little initial momentum. Moreover, 

 the gas from liquid hydrocyanic acid is cooled almost to freezing 

 point on formation and consequently is decidedly heavier than the 

 hot, machine- or pot-generated product. As the molecular activity 

 of gases increases proportionately as the temperature, that of the 

 gas from liquid hydrocyanic acid is least when first generated 

 but increases as it attains the temperature of the air, while in pot 

 or machine generated gas the inverse is the case. Thus the initial 

 diffusion is slower in the case of liquid hydrocyanic and is attained 

 throughout the bottom of the tent sooner than at the top. 



Hydrocyanic acid gas being lighter than air, it has been natural 

 to suppose that the greatest density, signifying the highest mortality 

 among scale-insects, would be towards the top of the tent, and this 

 has been confirmed in the case of Dialeurodes citri (citrus whitefly), 

 Bruchus {Acanthoscelides) obtectus (bean weevil) and Calandra granaria 

 (granary weevil). Investigation into the employment of liquid 

 hydrocyanic acid has shown that with this method the scale-mortality 

 was more eSective towards the bottom of the tree than towards the 

 top. Tables show the results of this method in the case of Lepido- 

 saphes beckii (purple scale) and Chrysompkalus aurantii (red scale), 

 both of which bear out the above theory. A dosage schedule for 

 liquid hydrocyanic acid, which will necessitate many changes from 

 the present schedule based on pot generation, is being prepared. 

 Since the infestation of scale-insects on large citrus fruit trees is 

 usually most severe on the lower or more protected part of the tree, 

 the advantage of the liquid hydrocyanic acid fumigation is obvious. 

 Other benefits are the reduction in cost of apparatus, and in the cost 

 of tent repairs, the liquid acid being harmless to cloth. The treatment 

 of small trees can be performed with greater accuracy and certainty 

 of results, greater speed in treatment is possible, and the quantity of 

 hydrocyanic acid required may be slightly less than by the other 

 methods. Improvements are, however, required, in manufacture, 

 BO as to furnish a uniformly high grade product; in containers, 

 through the use of material free from chemical action with the gas ; 

 and in field application, to guarantee accurate delivery and complete 

 vaporisation of the required charge. Assurance has been given that 

 these faults will be corrected in the immediate future. 



Howard (L. 0.). Gracilaria zachrysa, Meyr. ; Corrective Note.— JZ. 

 Econ. Entom., Concord, N.H., xii, no. 1, February 1919, p. 124. 



Attention is drawn to the statement made in a recent paper, that 

 Gracilaria azaleae, considered identical with G. zachrysa, a pest of 

 apple foliage in north-west India, had recently been introduced into 



