422 



the midges are swarming in the greatest numbers. This depends 

 on the fact that the insects preferably oviposit on the spikes when 

 they are bursting, whereas fully developed spikes are seldom attacked. 

 On an average 5 per cent, of the flowers were destroyed by this pest. 



Teagardh (I.). Redogorelse for det Entomologiska Laboratoriets 

 Verksamhet under 1915-1917, [Report on the Investigation of 

 Forest Insects during 1915-1917 at the Entomological Laboratory 

 of the Swedish State Institute of Experimental Forestry.] — 

 Meddelande frdn Statens Skogsforsoksanstalt, Stockholm, Hafte 15, 

 1919, pp. 154-174, 5 figs. 



In investigations on the pine beetles {Myelojyhilus piniperda and 

 M. minor), the problems that have been studied include the 

 influence of the size of the felled trees on the development of the brood, 

 the ability of the beetles to disperse, the influence of the time when the 

 trees are cut and the consequent injury to the trees caused by the beetles 

 when feeding. It was found to be correct that the beetles will oviposit 

 on trees measuring less than \\ inches at the base, but that the larvae 

 are unable to complete their metamorphosis owing probably either to 

 the small space at their disposal, or to the too rapid drying of such 

 slender stems. In larger trunks, however, the number of imagines 

 that develop rapidly increases, being about 15 per each egg-gaUery in 

 trees of a diameter of 2f inches. Consequently, when thinning the 

 forest, the smaller trunks may be left without any danger of the 

 beetles increasing in number. When the beetles leave the trunks 

 in order to feed on the shoots, they invariably choose the nearest trees. 

 The damage to the crowns of pine trees is therefore usually concentrated 

 round the localities where the beetles have bred. As regards the 

 effect of the date of cutting the trees, it was found that there is a 

 period of at least two months during the summer when the pine trees 

 may be felled and left in the forest without any protective measures 

 being taken, such as removal of the bark. This is due on the one 

 hand to the fact that the pine beetles swarm early in the spring and 

 only have one generation a year, the trees feUed after the swarming is 

 over consequently escaping oviposition, and on the other hand to 

 the fact that trees felled during the earlier half of the summer do not 

 attract ovipositing beetles in the following spring. The measurements 

 taken in order to ascertain whether the injury caused to the shoots 

 results in reduction of the growth of the trees failed to show any 

 decrease. In the cases investigated, however, the attack had only 

 taken place during one year. Investigations on the spruce bark-beetle 

 {Ips ty2Jographus) and on the enemies of spruce-cones have already 

 been noticed [see this Review, Ser. A, vi, pp. 90, 287]. 



Tragardh (I.). Skogsinsekternas Skadegbrelse under Ar 1917. [The 

 Injuries caused by Insects to Swedish Forests in 1917.] — 

 Meddelanden frhn Statens Skogsforsoksanstalt, Stockhohn, Hafte 16, 

 no. 4, 1919, pp. 67-114, 14 figs. 



The birch bark-beetle {Scolytus ratzehurgi, Jans.) does not seem to 

 play any important part in Sweden, as a rule attacking only isolated 

 trees. At Vaesby in Oland, however, in 1915, about 500 birches were 

 so severely injured that they had to be cut down. An investigation 



