555 



Marie (M. P.). Destruction des Scolytidae par les Arbres-Pieges dans 

 les Exploitations de Coniferes. — Bull. Soc. Path. Veg. France, 

 Paris, ix, no. 2, April-June 1922, pp. 120-124. 



While trap trees for the destruction of the Coleoptera that live in 

 the bark of forest trees have been in use for a considerable time, no 

 very detailed instructions for their practical employment seem to 

 have been published. It has been noticed that not only do these 

 xylophagous insects pi^efer sickly or recently felled trees for oviposition, 

 but also that a female bred from a dying tree, or a tree felled during 

 the winter, has a reproductive capacity almost double that of one 

 developed on a healthy tree. Experience has shown the necessity of 

 decorticating felled trees ; otherwise the Scolyticl infestation will 

 increase until the entire coniferous stand may be destroyed. The 

 following treatment has been found to give a large measure of success 

 during the first year, and practically complete success after the second, 

 provided that the procedure is correctly carried out. The first trees 

 to be used as traps should be cut down in winter and left on the ground. 

 As soon as the warm weather begins, oviposition punctures, which are 

 easily visible, should be searched for on the felled trunks. Six weeks 

 after these are first observed, when all oviposition of the various 

 species of bark-beetles may be expected to have been completed, the 

 felled trees should be removed to the edge of the wood, decorticated, 

 and the bark burnt on the spot. This treatment should be repeated in 

 summer, by felling a new series of trap trees at the end of July and 

 removing them in September, in order to destroy a possible second 

 generation. 



If the infestation begins in small patches, involving a few trees only, 

 those that show signs of infestation by turning yellow should be 

 examined for larval galleries by removing small pieces of bark ; if 

 any are found, the trees attacked should be removed, decorticated and 

 the bark burnt. Then, during the winter, two or three healthy trees 

 should be cut down in the infested areas to act as traps and the 

 treatment described above followed ; two further trees being then 

 felled to trap any insects surviving on adjacent trees. This treatment 

 is generally effective in the first year. 



If the infestation is general, but not very severe, all affected trees 

 and all obviously sickly ones should be removed and the bark taken off 

 and burnt ; in the winter a first series of trap trees should be felled 

 throughout the plantation, and again in summer as described above. 

 This treatment should be followed for two years, felling in each year 

 three to four per cent, of the trees for spring traps and two per cent, for 

 the summer traps. 



In cases where infestation has already exceeded 20 per cent, of the 

 trees the plantation is doomed, and it is best to cut down all the trees 

 at once before the healthy ones have lost their marketable value. In 

 old plantations, where the trees are aU more or less infested and have 

 ceased growth and show signs of weakness due to age, as, for example, 

 in ornamental stands that it is desirable to preserve as long as possible, 

 the methods outlined above are applicable, but the number of trap 

 trees used must be at least 10 per cent, of the total stand, with another 

 five per cent, for the summer traps. Even then, the difference between 

 the felled trees and the sickly ones in the stand is not sufficient to 

 attract all infestation to the traps. 



(7933) 2 P 2 



