REMEDIES AGAINST BARK-BEETJ.ES. 29 



cated in places and otherwise wounded, so that the beetles can gnaw 

 into the wood or inner bark, lay their eggs, and thus finally form brood- 

 galleries. 



Eichhoff asks the pertinent question: "How do great numbers of 

 bark- beetles pass into regions where perhaps before they were scarcely 

 known by name? For example, at the end of a period of fifty years, 

 all at once Tomieus curvidens appeared in the Botanic Garden of the 

 University of Vienna, and were very destructive to diflterent exotic 

 cedars, larches, etc., afterwards attacking white tirs, which contained 

 numbers of the beetles. 



The bark-borei'S, especially Tomieus typographus, belong to those in- 

 sects which sometimes produce extensive devastations by immigration 

 from without. According to a German writer they doubtless migrate 

 for short distances, since not seldom there result local destruction of 

 groups of firs when previously no bark-borers were to be seen. It is 

 also certain that forests previously entirely free from bark-beetles be- 

 come infested by bark-beecles bred in wood and lumber yards. It is 

 difficult and questionable how far such an immigration may extend. 

 An example of an extensive emigration of Tomieus typographus is 

 afforded by H. Tiedemann in the province of Xishny- Novgorod. 



In the midst of an imperial forest of about 2,500 ha lying in the district Arsamass, 

 and composed almost exclusively of hard-wood trees, dccur two fir-growths of 5(^, 

 perhaps 60, ha in extent. In both there was no windfalls, no burnt areas, but a good 

 close growth in which no bark-borers had appeared. Suddenly in the year 1883 ttie 

 bark-borers were so numerous that 2,000 fir trunks at once fell, and had to have the 

 bark stripped otf and burnt. The appearance of the bark-beetles is in this case only 

 to be explained by their flying into this area. The nearest fir-growths are from 15 

 to 20 kilometers distant, and those of sufficient size to aflford time for the infection of 

 the fir-growths in question, about 50 kilometers distant. 



Perhaps the best method o preventing or stopping the work of bark- 

 beetles is that of a Frenchman, M. Eobert, given in the Gardener's 

 Chronicle and quoted by Miss Ormerod: 



The best remedy appears to be that adopted with great success in France by M. 

 Robert, after careful observation of the circumstances which stopped the operations 

 of the female beetle when gnawing her gallery for egg-laying, or which disagreed 

 with or destroyed the maggots, and is based in part on similar observations of the 

 effect of flow of sap to those noticed in England by Dr. Chapman. 



It appeared on examination that the grubs died if they were not well protected 

 from the drying action of the air; on the other hand, if there was a very large 

 amount of sap in the vegetable tissues that they fed on, this also killed them ; and 

 it was observed that when the female was boring through the bark, if a flow of sap 

 took place she abandoned the spot and went elsewhere. It was also noticed that the 

 attack (that is, the boring of the galleries which separates much of the bark from 

 the wood) is usuallj' under thick old bark, such as that of old elm trunks rather 

 than under the thinner bark of the branches. Working on these observations, M. 

 Robert had strips of about two inches wide cut out of the bark from the large 

 boughs down the trunk to the grouud, and it was found that where the young bark 

 pressed forward to heal the wound and a vigorous flow of sap took place that many 

 of the maggots near it were killed, the bark which had not been entirely undermined 

 was consolidated, and the health of the tree was improved. 



