1903.] E. P. Stebbing — Economic Entomology. 81 



We have seen that the study of Economic Entomology first pies* 

 cribes a knowledge of the life-histories of noxious pests and that this is 

 the first work to be taken in hand. Having made ourselves acquainted 

 with these, we are now in a position to consider what remedies may be 

 introduced to combat them. 



It may be said, the question has been pertinently asked very often, 

 ' But why bother about remedies from whose introduction a very pro- 

 blematical good is to be derived, when India has gone on all these years 

 without them' ? I would retort that the world went on for a good many 

 centuries without the telegraph and railway, that Englishmen managed 

 to exist in some comfort in Calcutta for considerably over a century 

 without the electric fan and light and yet no one doubts their useful- 

 ness and necessity at the present day. The agricultural require- 

 ments of the country have not stood still ; they have advanced. The 

 study of the science under consideration has become of such importance 

 owing to the large increase in the cultivated tracts in the country and to 

 the much larger development in this respect which the great irrigation 

 schemes promise. It is an axiom in Economic Entomology that to increase 

 the food-plant of an insect over large contiguous areas is to increase the 

 numbers of the pest itself since finding so much of its favourite food 

 close together enables it to increase with ease, the usual checks it would 

 have to overcome in its natural surroundings being absent. It will 

 be obvious to everyone that a large irrigation scheme will help the 

 insect to perfection. We come then to the question of remedies. 

 Remedial measures divide themselves into two groups : — 



(1) Those applicable through the agency of man. 



(2) Those which Nature herself puts into force to prevent, or bring 

 down to normal proportions, undue increases of any particular members 

 of her animal kingdom. 



The first group, the question of remedial measures to be introduced 

 by man's agency, will be considered in detail later on, but we may show 

 briefly here en passant how the knowledge of the life-history leads to, or 

 suggests one class of remedy to be employed. We have seen how the 

 mouth parts in insects vary, some being furnished with a biting mouth, 

 whilst others have a sucking one. Now the presence of one or the other 

 of these forms of mouths will decide, in the case of the insecticide sprays, 

 the nature of the spray to be used. The obviousness of this will be 

 evident when it is mentioned that some spraying mixtures are merely 

 contact ones, whereas others must be taken internally to have killing 

 effects. The first are used against sucking insects which have usually 

 soft bodies, their spiracles, or air-breathing openings at the side of the 

 body, being large and exposed. It is useless using a poisonous spray 



