287 



Traoardh (I.). Oversikt over Skogsinsekternas skadegorelse under ar 

 1916. [Review of the Forest Insects of Sweden in 1916.] — Stamens 

 Skogsfdrsdksanstalt, Slockholm, Flvgblad no. 10, 1918, 28 pp., 

 13 text-figs. 



A collation of the data regarding the injnry caused by the pine 

 beetles, Mijelophilus pii'uperdn and M. htdnor. shows that their attacks 

 were most in evidence in Giivle-Dala and the Eastern and the Southern 

 districts. The common reports that these pine beetles are spreading 

 must not be taken literally ; they show however that owing to the 

 thinning of the pine forests, which is practised to a greater degree 

 every year, the facilities for the propagation of these pests have greatly 

 increased. In the southern part of Sweden the injury caused bv the 

 beetles, when feeding in the crown of the pine treevs, does not seem 

 to imperil the health of the trees, but in the northern part of the country 

 this kind of injury appears to be more dangerous. 



Ips typograpluis and Pitijogenes chalcograpJius were most in evidence 

 in Hernosands districts, where 70 per cent, of the reports dealt with 

 these pests. Middle Norrlands, Giivle-Dala and the Eastern district 

 following with about 50 per cent. In many reports the ravages were 

 comiected with previous damage of the forests caused by snow and 

 storms. Old trees and those of medium age were preferred, and the 

 attacks did not spread over larger areas than groups of a few hundred 

 trees, the next generation migrating elsewhere in large clouds. There 

 are no data as to the time of swarming or for the time required for 

 the development of one generation, but Kolmodin's investigations 

 showed that in 1914 in Orsa the first generation of Ips Igpograpluis 

 required about 70 days from the 16th of May to the 24th of July. 

 During the last half of the summer other swarms were observed, and 

 it is therefore reasonable to suppose that in the autumn the larvae 

 of the second generation were full-gi'o\ni or had even pupated. In 

 the spring of 1915 the spruce bark-beetle was therefore far more numer- 

 ous than is usually the case. As a rule in the Eoyal forests attempts 

 have been made to combat the beetle, but many private owners 

 entirely neglect any preventive measures. It therefore seems probable 

 that it may become necessary to adopt legal measures in order to 

 enforce the work necessary to control this pest. 



Bupalus piniari)is has been reported from several localities. A 

 review of the geographical position of the localities where ravages 

 caused by this moth occurred during the years 1889-1916 elicits 

 the fact that they are nearly all situated in the Eastern part of the 

 country. The annual rainfall decreases gradually from west to east 

 in Sweden and the outbreaks have occurred only in the driest part of 

 the country, which seems to suggest that a low rainfall favours the 

 propagation of this moth. If this assumption were correct, the years 

 prior to an outbreak might be expected to be those of abnormal drought. 

 An analysis of the precipitation over certain periods shows this hypo- 

 thesis to be accurate, the amount of rainfall in all the cases analysed 

 having decreased by from 15 to 27 per cent, of the normal during 

 2 or 3 years before the outbreak. The' author suggests that the 

 reduced rainfall favours the increase of the moth in that the fungoid 

 diseases that generally attack the hibernating larvae are checked 

 when the soil becomes too dry. 



