so INJURIOUS AND USEFUL INSECTS 



This beetle is beset by many insect-parasites. Ichneumons 

 and allied Hymenoptera lay their eggs in the larva, and 

 Taschenberg enumerates thirteen different insects which have 

 been bred from it. 



Various remedies have been proposed for the extermination 

 of the elm-bark beetle, such as bands of coal-tar, to prevent 

 the beetles from climbing the trunks, vigorous paring of the 

 outer bark, and the felling and burning of all infected elms. 

 It is to be noted that for upwards of sixty years entomologists 

 have called attention in the most emphatic language that they 

 can command to the danger of leaving felled elm-trees long on 

 the ground. The trunks of such trees nearly always become 

 infested by bark-beetles, and furnish a perpetual supply for the 

 infection of sound trees. The plague has become so widespread 

 that very drastic measures are called for, if it is to be effectively 

 checked. Under present circumstances single plantations of 

 elms can hardly be protected without the most vigilant attention. 



Another and smaller species of Scolytus (S. multistriatus) is 

 sometimes found on the elm ; its maggot-galleries radiate much 

 more regularly than those of S. destructor. Other species 

 attack the birch, the oak, and the plum. Pines are attacked 

 by allied species of bark-beetles, such as the Tomicus typo- 

 graphus, which has caused great loss in the forests of Germany. 

 The forestry departments have now learned how to keep its 

 devastations within bounds. Either trees already infected or 

 sound trees are felled at the time when the beetles are expected 

 shortly to appear. Sometimes they are only ringed at first, 

 being felled some weeks later. These trees are selected in 

 preference to uninjured standing trees by the beetles, and when 

 they are well-stocked with larvae, the bark with all its popula- 

 tion is stripped off, and scrupulously destroyed. The German 

 foresters call the felled trees Fangbdume or beetle-traps. The 

 successful treatment of what was locally known as the " bark- 

 beetle calamity" of Bohemia in 187 1-5 is a model for all 

 foresters, who may be called upon to contend with similar 

 plagues.* 



There are many true weevils (p. 44) whose larvae burrow 

 beneath the bark of trees. These beetles lay their eggs outside 

 the tree, in surface-cracks, and make no mother-galleries 

 (see p. 48). 



* The story is related by AUum, lot:. ciL, p. 295. 



