480 



same threshold of development (50°) for the pupa as for the egg or 

 larva ; this gives a figure of 265 for the pupa. 



Apart from variations caused by measurable factors, the constants 

 still varied from 156 to 170 for the incubation period, from 527 to 873 

 for the larval period, and from 256 to 274 for the pupal period. 

 Thus the effective day degrees of the three periods added together 

 are from 939 to 1,317, with an average of 1,101. In taking the entire 

 development as observed in 200 individuals, the minimum effective 

 day degrees amounted to 950, whereas where records were kept of the 

 first appearance of each stage the minimum appeared to be 1,027, 

 To the numbers 939 and 950 another 50 day degrees may be added 

 to allow for the accumulation between the emergence of the adult 

 and oviposition ; the minimums are therefore 989, 1,000 and 1,027, 

 with an average of 1,005. The first individuals of a given brood may 

 therefore be expected when 1,000 effective day degrees have accumu- 

 lated after the appearance of the first individuals of the previous brood. 



A spray programme is given based on the relation of accumulated 

 effective day degrees and the time of the appearance of the first larvae 

 of each generation, providing three sprays for the first, and two for 

 each of the sulisequent two broods, the first spray being applied when 

 about two-thirds of the petals have fallen. 



Sasscer (E. R.) & Weigel (C. A.). Fumigation with Hydrocyanic- 

 acid Gas in Greenhouses on a Commercial Basis. — //. Econ. Enf., 

 Geneva, N. Y., xv, no. 3, June 1922, pp. 200-203. 



Hydrocyanic acid gas fumigation is an effective means of con- 

 trolling the more important insect pests in greenhouses without 

 appreciable injury to the plants, provided the necessary precautions 

 are observed. Experiments have been carried out against Trialeurodes 

 vapor ariornm, Westw., on Ageratum ; Thrips tahaci, Lind., on 

 carnations ; Coccus hesperidmn, L., on Laura nohilis ; Ortliczia 

 insignis, Doug., on miscellaneous plants representing 101 genera ; 

 Saissetia olcac, Bern., on miscellaneous plants representing 15 

 tropical genera ; Euthrips orchidii, Moult., on orchids ; Ischnaspis 

 longirostris, Sign., on miscellaneous palms ; and Typophoriis (Paria) 

 canellus, F., on roses. The fumigant used was made up of 1 oz. 

 avoirdupois of sodium cyanide (containing approximately 51 per cent, 

 cyanogen), 1| liquid oz. of sulphuric acid (1-83 specific gravity), and 

 3 liquid oz. of water. To secure an equal distribution under green- 

 house conditions it is necessary to use a number of generators. If 

 used persistently, weak doses will control all common greenhouse 

 insects without reducing the market value of the plants. The dosages 

 tested varied from J to 5 oz. according to the nature of the plants. 

 Some plants, such as orchids and carnations, may be safely fumigated 

 while in bloom without injury to the flowers. 



Crawford (H. G.) & Spencer (G. J.). The European Corn Borer 

 {Pyrausta nubilalh, Hubn.) : Life History in Ontario.— J/. Econ. 

 Enf., Geneva, N. Y., xv, no. 3, June 1922, pp. 222-226. 



An account is given of the seasonal history of Pyrausta nuhilalis, Hb., 

 under laboratory and field conditions in Ontario, also a list of food- 

 l)lants other than maize. The date of sowing and the degree of 

 infestation were found to be closely correlated, both in experimental 

 and field conditions [R.A.E., A, x, 385]. 



