STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 49 



and Ihe greenhouse white fly {Aleyrodcs vapor arionim) often transmits 

 the disease Cladosporiuni fulviim to tomatoes. 



Tree crickets {QLcanthus) are said to be responsible for the inocula- 

 tion of trees and shrubs with canker, of raspberries with the cane 

 blight, and probably for the production of other diseases. 



Insects and Disease 



(Consult Handbook of Medical Entomology by Riley and Johannsen, and 

 Medical and Veterinary Entomology by Herms.) 



During the last twenty years important discoveries have been made 

 regarding the transmission of certain diseases by arthropods such 

 as the mosquitoes, house-flies, stable-flies, gad-flies, tsetse-flies, fleas, 

 bed-bugs, lice and ticks. 



Insects and arachnidans cause disease in one or more of the fol- 

 lowing ways: by direct infection, that is by the introduction of a patho- 

 genic organism into the circulation, as in the case of the malarial 

 mosquito, the yellow fever mosquito, the sleeping-sickness flies, 

 horse flies and others; by indirect infection, that is by infecting food, 

 as in the case of the house-fly; by internal parasitism as in the case of 

 warble flies and bots; by external parasitism as in the case of lice, 

 fleas, bed-bugs and ticks ; and by the introduction of poisons as in the 

 case of bees, wasps, kissing bugs and others. 



Brues and Sheppard have divided the diseases that are carried by 

 insects into three groups: 



Group A. — Characteristically insect-borne diseases. 



Group B. — Often insect-borne diseases. 



Group C. — Possibly insect-borne diseases. 



Under Group A are included malarial fever, yellow fever, filariasis, 

 sleeping sickness, typhus fever, bubonic plague, African tick-fever, 

 Rocky Mountain spotted fever of man, and Nagana and Texas fever 

 of horses and cattle. 



Under Group B. are included typhoid fever, cholera, dysentery, 

 diarrhoea, tuberculosis, septicaemia. 



Under Group C. are included anthrax, rabies, pellagra, hookworm, 

 beriberi, black water and relapsing fever of man; and equine infectious 

 anaemia. 



