7R E. P. Stabbing — Economic Entomology, [Apt?- 



of budding girlhood be traced in the baldheaded, toothless, newly-born 

 babe. Both are slowly developed. The insect commences life as an egg. 

 From this egg hatches out a grub which in form is often totally unlike the 

 future adult. It is in this grub stage that all increases in size 

 usually take place. The grub changes to a pupa or chrysalis, a resting 

 stage, during which the insect does not feed and usually remains quies- 

 cent. In this stage of rest the internal complex organs arrive at matu- 

 rity and the wings are acquired. When this development is complete 

 the insect emerges in its adult or perfect form and subsequent to this 

 all further growth ceases. Any common butterfly goes through these 

 changes. This state of affairs is, however, not always fully carried out, 

 as in some Orders of insects the third or pupal stage is absent. In these 

 cases the young ones on hatching out from the egg usually resemble the 

 parents in form, but not in size ; the wings are always absent and coloura- 

 tion and markings may undergo modifications. Such insects acquire their 

 wiugs and full size by a series of moults, the outer skin being shed at 

 intervals, the last moult producing the perfect insect with fully-deve- 

 loped wings. The common North-West or Migratory Locust (Acridium 

 peregrinum) is an instance of this mode of growth. There is one 

 more point in connection with the structure of insects to which 

 attention must be drawn, a most important one since, as we shall see 

 later on, on it depends the nature of the remedies we bring into force to 

 combat serious attacks. This important point is the form of the 

 mouth parts that may be present. In this respect insects may be 

 roughly divided up into three groups according as to whether they have 

 a mouth formed for biting, for sucking, or a combination of the two. In 

 the biting mouth, biting jaws or mandibles are present, by means of which 

 the plant tissues are bitten through before being devoured. Instances of 

 such a mouth may be seen in the locust or any common beetle. In the 

 sucking mouth the biting jaws are absent or are mere rudiments and the 

 mouth consists of a long tube or proboscis often furnished with one or 

 more piercing organs to enable the insect to pierce through tissues of 

 plants and then insert the tube and suck up the sap. Bugs, plant lice, 

 and scale insects have such a mouth. In the biting and sucking mouth 

 both mandibles and the sucking tube are present, as may be seen in the 

 common bee. As I have said, these different forms of mouth bear a con- 

 stant and definite relation to the method of life and feeding operations 

 of the insect and therefore to the methods that can be introduced to 

 combat its attacks. We are now in a position to consider the first step — 

 the study of the life-histories of pests. 



It may be taken as a cardinal point in remedial work that the more 

 one knows about the habits and life-history of a given species of insect 



