MAN IN A WORLD OF INSECTS — DE LONG 433 



fields of corn and wheat, orchards of fruits, fields of potatoes, peas, 

 and tomatoes, vineyards, citrus groves, and all other types of crops. 

 Some wood-boring insects attack and fell our forest trees. Others 

 inject disease-producing organisms into certain trees, causing Dutch 

 elm disease, phloem necrosis, or oak wilt, which take their toll of our 

 forest and shade trees. Lmnber used in buildings is continuously 

 attacked and destroyed by termites and powder-post beetles. 



iTisect-home diseases of man. — The most direct and fatal attacks are 

 by those insects which feed upon the blood of man. The world health 

 authorities, working through the United Nations and gaining knowl- 

 edge and statistics from all the nations of the world, are authority 

 for the statement that insects are the cause of one-half of all human 

 deaths, sickness, disease, and deformity. 



The anopholine mosquitoes alone are responsible for injecting into 

 man's blood stream the protozoans which cause malaria — a scourge 

 which infests one-sixth of the human race and kills somewhere in the 

 world a man or woman every 10 seconds. In like manner the Aedes 

 mosquitoes are vectors of organisms causing yellow fever, a much 

 more deadly human disease although not as widely distributed 

 throughout the world. 



The Simulium or black flies, which occur in certain tropical areas 

 aromid the world, inject into man's blood the microfilaria romid worms 

 causing blindness (onchocerciasis) in man. Large segments of the 

 native populations are often totally blind. 



The tsetse fly is one of the most deadly of the blood-sucking flies, 

 causing the usually fatal sleeping sickness in man. Several million 

 square miles of Africa have been so completely dominated by this 

 insect that man has not been able to inhabit this area. The wild game 

 animals serve as reservoirs for the trypanosomes which are carried to 

 man by these flies. 



REASONS FOR THE SUCCESS OF THE INSECT WORLD 



What is the character of these rivals which humanity must surely 

 hold in check if it is going to be successful as a species ? The follow- 

 ing reasons could be cited to explain why the insect type has become 

 so highly evolved, adapted, selected, and so dominant and successful 

 on the surface of the earth : 



1. The body is enclosed within an exoskeleton which is composed of 

 chitin. Its essential chemical elements, carbon, hydrogen, and nitro- 

 gen, are easily and abundantly available from green plants in the form 

 of nitrogenous sugars. A body covering of this type limits the insects 

 to small size but affords great strength due to direct muscle attach- 

 ments. It also favors diversified mutation and all types and extremes 

 of protection through form, color, and thickness of the armor. This 

 skeleton is always properly developed, insofar as diet is concerned. 



