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Tragardh (I.). Undersokningar over den storre Margborren, dess 

 Skadegorelse och Bekampande. [Investigations on Myelophiliis 

 piniperda, its Injury and Control.] — Medd. Stat. Skogsforsoksanst., 

 Stockholm, xviii, no. 1 , 1921 , pp. 1-80, 27 figs. [With a Summary in 

 German.] 



Owing to thinning methods increasingly employed in Sweden 

 during the past 10 years, Myelophiliis piniperda has become more 

 abundant in forests. 



Experiment has shown that this bark-beetle has only one annual 

 generation ; under certain undetermined circumstances it is able to 

 produce a second brood which is of no practical importance owing to 

 its rare occurrence and small numbers. In Southern and Central 

 Sweden, up to 64° north latitude, swarming takes place at the end of 

 May or early in June. 



The injury done at the beginning and in the middle of June is at 

 first difficult to detect ; the affected needles are distinguishable only 

 by the fact that they are shorter. The shoots then resemble those 

 injured by the pine shoot moth [Rhyacionia hioliana], except that in 

 the latter case the openings surrounded by resin are missing. Dry 

 shoots still on the branch are often infested by larvae of Anobimn sp., 

 but this beetle is never a primary pest. If the shoot is so vigorous that 

 the outer woody portion is not destroyed, the injured part is healed by 

 the formation of a callosity, though growth remains checked during 

 the year first following. The crowns are attacked in spring by beetles 

 that have not matured in the previous years. This injury is less severe 

 than that in June caused by individuals that have produced the new 

 brood and are preparing to produce a second one, or than that in July 

 due to the new brood. The rare occurrence of the second brood 

 just mentioned has not been explained, but it may be due to the lack 

 of suitable trees for the breeding of this second generation. It thus 

 seems that feeding after the production of the annual brood aims at 

 forming a reserve brood able to utilise any breeding facilities that may 

 appear in late summer. 



The top of the crown is the part most attacked, probably because 

 M. piniperda prefers the same year's or the previous year's shoots to 

 older ones. Injury due to a single attack may be made good by new 

 shoots, but nevertheless gives rise to loss, and it has been estimated 

 by a competent authority that in extreme cases the increase in diameter 

 of the tree may be lessened by 22 per cent. Figures are given showing 

 that a 10 per cent, reduction entails a loss of about 1,600,000 cubic feet 

 of timber in Sweden. It is very seldom, however, that trees in a 

 plantation of young pines are killed as the result of one attack. The 

 injury to the trunk as a result of mining for breeding purposes varies 

 in importance. If the mines are numerous the tree may be killed ; 

 if their number is small it is possible that the tree may escape infesta- 

 tion in the following year. In an experimental plot 6 per cent, of the 

 trees were killed and 6 per cent, were fatally injured in the course of 

 two years as a result of the winter feeding. As the latter occurs as fre- 

 quently as the injury to the crowns, its importance appears to have been 

 overlooked hitherto. More attention should be paid to this phase 

 of the activity of M. piniperda. 



If the trees felled in a thinned area are left lying in the forest 

 the crown infestation spreads throughout it, but if the felled trunks 

 are placed along a road most of the fresh injury is confined to the 

 trees alongside, indicating that M. piniperda seeks trees that are close 



