144 Control of Parasites 
Mechanical Destruction of Insects. A large number of 
insects, among which are some of the most injurious, can- 
not be reached by insecticides, and even with those which 
can be so combated, it is often impracticable to attempt 
this method. Where 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 quiescent stage of develop- 
ment, namely, in the egg or pupa 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 trapped 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 quite practicable with all those insects which are 
ascending or descending the trunks. Such bands are merely 
a mechanical barrier to the progress of the caterpillars, 
which can then be brushed off 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 
1 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, 
