crop, natural agencies sooner or later step in and again reduce 

 the numbers of the pest and in consequence the damage done 

 by it to more reasonable proportions. Thus over a term of 

 years a balance is more or less preserved. In times gone by 

 this natural control was perhaps sufficient to meet commercial 

 needs, but now with keen competition and the call for high 

 quality and high yield, the average damage due to pests is 

 more than the industry can bear. It is therefore necessary 

 to add artificial measures to the natural agencies already at 

 work. Any consideration of such measures would, however, 

 be incomplete without some further reference to the chief 

 agencies of natural control i.e., weather conditions, the 

 attacks of other insects, and of birds. 



Of these agencies, the weather admits of no interference 

 on behalf of fruit-growing, but there is some hope that in years 

 to come a greater knowledge of the effects of weather on insects 

 may make it possible to predict the appearance or absence of 

 serious epidemic pests, and so enable measures against them 

 to be taken in time. Work to this end is going forward. 



As regards birds, the pros and cons of protection, legal and 

 voluntary, are gradually being placed upon more sure and 

 sensible foundations, and there is no doubt that insectivorous 

 species are among the very best friends of the fruit-grower 

 and therefore to be encouraged whenever possible. At the 

 same time the conditions of modern fruit-growing and agricul : 

 ture, with the necessity for destroying weeds and clearing up 

 overgrown hedgerows, limit to some extent the chief means 

 of encouraging the more useful birds (by the provision of suit- 

 able breeding places). It seems clear therefore that useful as 

 birds are as allies, it will never be possible to rely upon them 

 alone for winning the fight against insect pests. 



The remaining great natural factor in regulating the number 

 of pests is found in beneficial insects that is to say, those 

 insects which prey upon others. Such insects are always of 

 great value and are sometimes of overwhelming importance in 

 saving fruit trees from their enemies, and of all natural means 

 of control they perhaps offer the most scope for human inter- 

 ference. It is, however, not yet possible to increase beneficial 

 insects sufficiently to render the use of purely artificial methods 

 of control unnecessary, and in the case of practically every 

 pest some such measure as spraying is required. In this con- 

 nection it cannot be too strongly emphasised that artificial 

 control not seldom results in the destruction of both friend and 

 foe together, and that, tEerefore, having once taken over a 

 responsibility from Nature, the work must in future be 

 thorough or epidemics may be even more frequent than they 

 were in 'former times, when matters were left to take an 

 entirely natural course. 



