190:}.] E. P. Stebbing — Economic Entomology. 79 



the better are the chances of discovering a cheap and efficient remedy 

 for controlling it. 



Many insects, for example, can be dealt with only in the active 

 feeding condition ; with others the eggs are the easiest destroyed, whilst 

 in others again the quiescent or over- wintering stage is the easiest 

 disposed of. We must therefore be able not only to recognise it in its 

 different stages, but must know just how long it remains in each and 

 just how it comports itself in each. Eacb new insect which makes 

 itself unpleasantly prominent must be studied throughout its life 

 round before we can say that we know best how to fight it, and when 

 commencing the work in a new country this investigation into the 

 pest's life-history is the point from which we must start. 



I have said that the Insect must be studied throughout all its 

 stages of egg, grub, pupa and adult, i.e., through its life cycle, and this 

 in itself is no light task, as it requires high powers of observation and 

 much patience in investigation work, which may have to extend over 

 several years. 



Unfortunately, however, when the life cycle has been watched 

 through the work is often by no means complete for the particular 

 insect under surveillance may pass through several such in the year, 

 and this is more particularly the case in tropical countries. In our own 

 Northern clime (England) some insects in favourable seasons may 

 pass through two life cycles in the year — one in the spring or early 

 summer, a second in the late summer or autumn. But this is nothing to 

 what happens in tropical countries. In such the life cycles are greatly 

 increased and three, four, or even as many as seven or more, generations 

 of a pest may be run through in the one year and to add to the per- 

 plexities and worries the study of such entails the insects of the 

 various generations or cycles may vary in appearance, sometimes in a 

 marked degree. For example, many Indian butterflies have received 

 different names from eminent scientists owing to their great variations 

 in markings, colouration, and even shape in the various generations 

 they pass through in the year; the subsequent study of their life- 

 histories has shown them to be but the spring and summer forms of 

 one and the same insect. Thus the Economic Entomologist is able to 

 helpand set right the work of his museum comrade. But this forms 

 by no means the sum total of the vagaries of Insect life. We have 

 seen that an Insect may have several life cycles in the year the 

 individuals in which may vary in colour, shape, etc. But others go 

 further and spend one of their life cycles on one portion of a plant, 

 e.g., on the leaves and twigs above ground; whilst the other is 

 totally unlike the first in appearance and may be spent on the roots. 



