144 Control of Parasites 



Mechanical Destruction of Insects. A large number of 

 insects, among Avhich are some of the most injurious, can- 

 not be reached l)v insecticides, and even witli those which 

 can be so combated, it is often imj;raclicable to altemj)t 

 this method, ^^'here it is impossible to apply the poisons, 

 or also in connection with their application, mechanical 

 means of destruction may be employed. This is usually 

 best done when the insect is in a c^uiescent stage of develop- 

 ment, namely, in the egg or pujm state, although in some 

 cases the imago or larva state is more accessible. 



These latter can also occasionally be trapped and baited. 

 Moths, for instance, can be tra]jped by strong lights, and 

 special traps for that purpose are manufactured, but, aside 

 from the fact that beneficial insects are also caught without 

 distinction, these traps are practicable only under condi- 

 tions which rarely prevail where shade or ornamental trees 

 are to be protected.' 



Baiting by confining a freshly issued female under a sieve, 

 when many males will be attracted and can be captured, 

 will also be rarely a practicable method. But the trapping 

 of caterpillars by the use of bands around the bole of the 

 tree is cjuite practicable with all those insects which are 

 ascending or descending the trunks. vSuch bands are merely 

 a mechanical barrier to tlie progress of the caterpillars, 

 which can then be brushed oil with wire brushes and burnt. 



The simplest band is one of cotton batting, eight to twelve 

 inches wide, long enough to go round the trunk and overlap 

 two inches. This is tied tightly around the trunk, so that 



' Lately a gasoline torch has been placed in the market, which it is pro- 

 posed to make effective by both light and heat. Its merits are still under 

 investigation, but it is probably not practical for use on large trees, even if 

 the heat could be so regulated as to kill the insects and not the cambium 

 of the tree. 



