89 



simultaneously on the north side. This fact must be taken into 

 consideration in connection with the study of departures from the 

 computed constant in the seasonal events of this species. 



The range of the mountain pine beetle, Dendroctonus monticolae, 

 Hopk., extends throughout the pine zones of the Pacific Slope and mto 

 Wyoming, Montana and British Columbia, with a range of altitude 

 from near sea-level on the shores of Puget Sound to near timber 

 line in the northern Rocky Mountains and Cascades, and to 10,000 feet 

 or more in the southern Sierra Nevadas. Food-plants include 

 western white pine, lodgepole pine, sugar pine and western yellow 

 pine. Normally only one generation a year occurs, but towards the 

 southern and lowest altitude range a partial second generation 

 occasionally follows; whilst towards the highest altitude from 2 to 3 

 years are sometimes required for the development from the first 

 eggs to the last beetle of one generation, in which case, owing to the 

 overlapping of the broods of one, two and three year generations, 

 no choice is left as to taking advantage of a critical period in which 

 control operations can be carried on. 



In the case of Chermes (Pineus) strobi, Htg. (pine bark louse or 

 spruce gall louse), which requires two food-plants for its development, 

 and allied species, remedial measures such as contact insecticides 

 should be applied, during the critical period of activity, which is always 

 coincident with the beginning of new growth on the infested pine and 

 the opening of the buds on the spruce. As this is the only reliable 

 guide to the time for spraying, departures due to local influences 

 need not be considered. 



With regard to the gall-making species of Chermes on blue and 

 Engelmann spruces there is a close relation between the opening of 

 the buds and the hatching of the eggs, the number of days departure 

 from the constant not being sufficient to indicate that they are due 

 to local influences. 



The critical period in the seasonal history of the Hessian fly 

 [Mayetiola destructor] is the period of its emergence in the autumn, 

 and it has been found that if wheat is sown at the close of the general 

 flight period of the fly, the danger of serious injury will have passed 

 by the time the wheat is above ground and exposed to attack. The 

 time of emergence is controlled primarily by climatic conditions and 

 secondarily by weather, local soil and topographical influences. A 

 fly-free date for different localities and for an average season may 

 thus be determined by the application of the biocHmatic law, by which 

 also farm practice in general may be adjusted to geographical require- 

 ments with a view to producing the best results. 



QuAYLE (H. J.), i. Fumigation with Liquid Hydrocyanic Acid. 



Gray (G. P.) & Hulbirt (E. R.). ii. Physical and Chemical Properties 

 of Liquid Hydrocyanic Acid.— Univ. Cal. Agric. Expt. Sta. 

 Berkeley, Cal, Bull. 308, June 1919, pp. 393-428, 4 figs. [Received 

 30th December 1919.] 



Liquid hydrocyanic acid, which was first used as a fumigant on 

 a commercial basis in 1917, has rapidly come into favour as an insec- 

 ticide. Under a tent the most marked killing-effect with the liquid 



