FIGHTING INSECT PESTS 187 



encircling of tree trunks with bands of some sticky substance 

 to prevent the crawling up of wingless insects have their 

 place in insect fighting. 



There still remains one other class of the so-called arti- 

 ficial remedies to be mentioned. They are really, however 

 natural remedies. These are all those included under the 

 general term of clean farming and high cultivation. The 

 result of their use is to make the plant better fitted to with- 

 stand the attacks of their insect enemies. In nature almost 

 all plants have to sustain more or less severe insect attacks. 

 It is naturally the weakest plants that succumb first. Where 

 man has gathered together many plant individuals of one 

 kind and has by that very act invited all the kinds of insects 

 that normally feed on these kinds of plants to come and 

 feast, he is, we might say, morally bound to protect his plant 

 wards from the too serious appetites of their guests. At 

 least he will be prudent if he recognizes this obligation. 



Insect pests of even more importance than those that 

 attack our crops and our forests, our clothes and our domes- 

 tic animals are those that bring suffering and death to our 

 own bodies by breeding and disseminating the germs of 

 human disease. 



The role played by insects in breeding and distributing 

 these animal disease germs, as well as bacterial (plant) germs, 

 has already been pointed out in Chapter XII. To fight 

 successfully these disease spreading insects, which is the 

 most effective way of fighting the insect-spread infectious 

 diseases, much has to be known of the structure, life-history 

 and general habits of the particular insect kinds involved. 

 The two most important kinds in our coimtry are mosqui- 

 toes, which breed and disseminate malaria and yellow fever, 

 and house flies, which spread typhoid and other bacterial 

 diseases. The fleas, which disseminate plague, are also of 

 great importance. 



The very best way to fight house-flies is to destroy their 



