1908.] 



The Elm Bark Beetle. 



617 



A severe attack of the Elm Bark Beetle (Scolytus destructor 

 Olivier) has occurred on the estate of the First Garden City at 

 Letchworth, Herts. About 50 elms have 

 The Elm been attacked on various parts of the 



Bark Beetle. estate, the species in each case being 

 Ulmus campestris. The beetle was first 

 noticed at work about three years ago, and since that time it 

 has spread considerably. Several trees, apparently in perfect 

 health twelve months ago, are now practically dead. In such 

 cases the holes made by the beetles can be seen all over the 

 bark. Trees which have been freshly attacked this year 

 show the presence of the beetle, even at a distance, by the 

 leaves on certain branches turning yellow. Some of the trees, 

 which are on a sandy soil, show the effect of the beetle by 

 losing their bark, which falls from the base of the trunk, but 

 those on clay show no sign of their bark peeling. 



Dr. R. Stewart MacDougall has furnished the Board with 

 the following report on this beetle : — 



" The large Elm Bark Beetle (Scolytus destructor Olivier) is a 

 very dangerous enemy of the elm. It attacks young and old 

 trees alike, and has now and again been the cause of the 

 destruction of many elms. The chief damage is due to the 

 tunnelling of the grubs. 



" Life History. — In very favourable conditions of weather 

 on the Continent, it is believed that two generations in the 

 year are possible. The same has been stated as possible in 

 Britain, but there is no experimental proof of this. Typically 

 one generation in the year is found. The adult beetles issue 

 in May or June, according to the position (north or south) 

 and to the weather conditions. Egg-laying follows, and the 

 grubs from the eggs bore their galleries between the wood 

 and the bark, the wood not being markedly tunnelled if the 

 infested part of the tree has thick bark. By the end of July 

 or in August many larvae may be full grown, and it is possible 

 that some pass on to pupation in time to admit of the exit of 

 the adult in the same autumn. More commonly, however, 

 pupation is delayed until the next April or May, the beetles 

 issuing in May or June. 



"Treatment. — 1. Where a tree is badly infested it should 

 be felled and the bark removed. The infested branches 



