6 



with one main object and that is to eat. The caterpillar 

 having eaten all it requires at that period of its life, turns to 

 a chrysalis, a stage in which the insect neither feeds nor 

 travels but undergoes great changes internally. From the 

 chrysalis comes the butterfly which, though it may sip a 

 little nectar, concentrates on breeding and spreading the 

 species. In each stage the foim of the insect is such as to 

 adapt it to one object at a time the caterpillar with its 

 jaws and absence of wings is fitted to do little else but feed, 

 the chrysalis must remain outwardly immovable, and the 

 butterfly with wings, with a trunk which does not allow of 

 its taking solid food, and with breeding organs well 

 developed, is clearly adapted to propagating the species. 



The bearing of all this on insect control is that it is very 

 necessary to be on the lookout for the different stages, which 

 though not in all cases as strongly marked as in the butterfly, 

 nevertheless always occur to a greater or less extent. 

 Obviously the stage when damage is likely to be done is 

 that adapted to feeding, but it serves equally well if the 

 pests are destroyed in one of the other stages. The great 

 thing therefore is to look for the condition in which the 

 insect is most vulnerable and to tackle it then, even though 

 at the time it may be doing no actual damage. Finally, in 

 connection with breeding, it may be pointed out that some 

 groups of insects such as Aphides (Green Fly) have found 

 it possible to do without males for many generations, the 

 females producing young without pairing, while in a few 

 cases (certain sawflies) males appear to have been nearly 

 lost altogether. This power of dispensing with males 

 naturally causes such insects to prove dangerous enemies, 

 for instead of about half the total population being able to 

 produce young, all can. Indeed throughout the insect world 

 it is possible to see how every development has been 

 regulated by the supreme necessity for rapid reproduction, 

 and it is this perpetual increase which so threatens the fruit- 

 grower . 



Nature's Control of Pests. The conditions under which 

 fruit trees are grown render them peculiarly liable to the 

 attacks of insect pests, for in the first place the fruit tree 

 is an artificial product which through cultivation has lost many 

 of the good constitutional features of wild trees, and 

 secondly the planting of large districts with the same kinds 

 of fruit enables a pest to penetrate throughout the area without 

 ever being at a loss for food. The reasons why, under con- 

 ditions so favourable to pests, fruit trees are not completely 

 overwhelmed is that the insects are to a considerable extent 

 kept in check by natural agencies. Thus, while for a year or 

 several years the destruction wrought by a pest may rise in a 

 wave which seems to threaten the very existence of a certain 



