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TragIrdh (Ivar). Vara vanligaste Barkborrar och deras Gangsystem. 

 [Our most common Bark-beetles and their Galleries.] — Statens 

 Skogsforsoksanstalt, Flygblad no. 8, February 1917, 28 pp., 

 27 text-figs. [Received 16th February 1918.] 



This paper is a popular treatise on the characteristic features and 

 systems of the galleries of bark-beetles, their feeding habits, choice 

 of trees, etc. 



The following species are dealt with : — Myelophilus piniperda, L., 

 M. minor, Htg., Hylastes ater, Payk., Dendroctonus micans, Kug., 

 Hylurgops paUiatus, GylL, Polygraphus poligmphus, L., Ips typo- 

 graphus, L., I. sexdentatus, Boern., Ljproximus, Eichh., I. acuminatus, 

 GylL, Pityogenes bidentatus, Hbst., P. quadridens, Htg., and 

 P. cJialcographus, L. 



Ips proximus is recorded for the first time from Sweden, where it 

 seems to be common. It has undoubtedly been previously overlooked 

 owing to its great resemblance to /. lands, and its occurrence has been 

 recorded under that species. 



Tragardh (Ivar). 0m de klimatiska Faktorernas inflytande pa Insek- 

 ternas upptradande. [On the Influence of Climatic Factors on 

 Insects.] — Sdrtryck ur Skogshogskolans Festsskrift 1917, StockJioIm, 

 1917, pp. 428-447, 7 figs. [Received 16th February 1918.] 



After an introductory discussion of the different factors influencing 

 the numerical variation of injurious insects, an attempt is made to 

 analyse the meteorological conditions during some outbreaks in Sweden. 



In the summer of 1911, Aphis (Siphonaphis) padi, L., did great 

 damage to cereals in southern Sweden. Tullgren, who described the 

 outbreak, suggests that the high temperature and the low rainfall were 

 the causes of the great increase in the numbers of this Aphid. An 

 analysis of the temperature during May-August in 1910 and 1911 

 shows, however, that the difference during these years was too small 

 to render it likely that the temperature played any important part. 



The difference in the rainfall during May- August, on the other hand, 

 was very marked, the total amount in 1910 being about 11| inches, 

 whereas in 1911 it was only about 6 inches or 53 per cent, of that 

 of the previous year. It is also notable that in 1910 heavy rains 

 occurred at the beginning of July at the very time that the Aphids 

 had just migrated from bird-cherries to the cornfields, where they 

 were more exposed. It therefore seems probable that in the summer 

 of 1911 the absence of the controlling factor exercised by high pre- 

 cipitation brought about the great increase in the numbers of this aphis. 



As regards Lymantria (Liparis) monacha, L., in Sweden and the 

 serious outbreaks of it in 1898-1902, it is of special interest to note 

 that it occurred not only in the chief centre in Kolmarden, but 

 simultaneously in other parts of Sweden, which at once suggests that 

 cHmatic conditions played an essential part. An analysis of the 

 temperature and rainfall during 1896-1898 elicits the fact that the 

 mean temperature in the neighbourhood of Kolmarden during xVpril- 

 August in 1896 and 1897 was about 3° F. higher, and nearly ^° F. 

 higher in Kristianstad, than in 1898. The rainfall during April-July 

 in 1896 was only 40 per cent, of that of 1897, and nearly the same 

 applies to Kristianstad for the years 1896 and 1897. 



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