SOME ASPECTS OF SPRAYING AGAINST PESTS. 
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SOME ASPECTS OF SPRAYING AGAINST PESTS. 
By A. H. Lees, M.A. 
[Read May 2, 1916 ; Dr. F. Keeble, F.R.S., in the Chair.] 
One is sometimes asked by somewhat irritated inquirers why " all 
these pests " which attack crops grown by man are so abundant, the 
implication being that in the good old days no such unpleasantnesses 
had to be faced. The question is an interesting one, and leads one 
to ask why there has been such an apparent increase in the number of 
enemies attacking horticultural crops. No doubt, crops had their 
enemies in bygone days, for who has not heard of the canker-worm 
and the palmer- worm of Biblical history ? In those days, however, 
" murrains " and similar visitations were looked upon as events 
altogether outside man's control, and as such to be accepted with 
as much equanimity as possible. At any rate, one may be sure that 
insect pests were present when there were no commercial plantations 
of fruit. Nevertheless it is obvious that not only has the number of 
kinds increased, but many kinds are found now in far greater numbers. 
There are several causes for this. The most important probably is 
the great increase of land planted with fruit. It is natural that 
where a district is found to suit fruit there fruit is planted, with 
the result that one may find in certain parts of England hundreds 
of acres where fruit plantations are practically contiguous. Under 
these conditions an insect living on fruit trees naturally flourishes. 
Food is abundant and easily accessible, so that such an insect, if 
occurring at first but on a single tree, will, in course of a few years, if 
unchecked, soon extend over the whole fruit area. Such a process can 
often be seen in action. The smaller winter moth, Cheimatobia brumata, 
has been known in the Evesham district for well over fifty years. It 
is present everywhere in that district, usually in great numbers. Sup- 
pose, however, one looked for this insect in a district where fruit- 
growing on a large scale was comparatively new. Should not one 
find a different state of things ? Seven years ago I was in the Wisbech 
district, where the spread of the winter moth could be observed. The 
moth was abundant in the gardens close to the town, but as one 
went farther out it became scarcer and scarcer as the gardens tended 
to become more and more scattered, till at a radius of five miles it 
was difficult to find. 
That was a case of an insect increasing owing to the increase in 
the density of fruit plantations. There is, however, another cause 
for the spread of insect pests, and that is through the transference 
of nursery stock from one district to another. I am aware that 
