SOME PHASES OF APPLIED ENTOMOLOGY IN SOUTH AFRICA. 261 



sciences of botany and bacteriology. An intimate acquaintance 

 with conditions is, of course, necessary. 



The science of applied entomology has made such rapid 

 strides during the last two decades, and so many new phases 

 opened for investigation, that one's chances of developing par- 

 ticular lines are boundless. Hewitt has written very effectively 

 on insect behaviour as a factor in applied entomology, and here 

 we have an example of what possibilities there are in developing 

 this line of attack . The response of the Mediterranean fruit fly 

 to a poisoned bait is but one instance of the factor, and opens up 

 a great future in insect control. 



We are accustomed to the use of certain chemicals and 

 compounds in our control work, but we must ever be on the 

 alert for new substitutes, which should be cheaper, and if possi- 

 ble, more efficient. Here the phase of applied entomology 

 touches the chemist more than the entomologist, but it is the 

 latter who sees the " end-point." 



The exact effect of insecticides, sprays, etc., on the plants 

 and trees is something we know little about ; the reaction of the 

 plant to the stimulus and stimuli calculated to produce desirable 

 reactions are points worthy of our consideration. 



Resistant varieties and disease-resisting plants is a subject 

 which the entomologist must ever keep in the limelight. The 

 use of northern spy stocks for apples against woolly aphis is 

 but one example of what I mean to convey. 



The question of parasites and parasitism is now, of course, 

 quite an important one in its bearing on economic entomology. 

 Last year Mr. Mally told us some facts about this phase. We 

 realize more and more 'each day the great part played by the 

 enemies of our injurious insects. Nor is it at home that we 

 must confine our search for these friendly insects ; the ex- 

 perience of other countries has taught us the value of going 

 abroad for parasites and predators. Parasitic fungi, bacteria or 

 other disease-causing agents liable to aft'ect our insect enemies 

 constitute an important subject in themselves. 



Ecology, or the interrelationship of animals and plants, is a 

 subject which has come into prominence recently. And it is 

 one which it behoves us to take into consideration. 



We have in our midst some injurious insects which have 

 come from other shores — a natural result of international com- 

 merce. Many of these are recognized troubles in their '' native 

 or adopted " lands, and have been the subject of much study. 

 But the fact of their having been investigated elsewhere need 

 not deter us from working on them here. Environmental and 

 other conditions account in many instances for great divergence 

 in the activities of insects. As well known as is the codling-moth 

 in the United States, it is still a constant subject for investiga- 

 tion on the part of eminent entomologists. 



However, it is in the realm of humanity that the entomo- 

 logist can find ample opportunity for his activities. I refer 

 now to the role which insects play in their relationship to man 



