56 ECONOMIC ENTOMOLOGY 



pneumonic plague passing from man to man directly, or conveyed by 

 insects. Dr. Kitasato is quoted as saying that the (Manchurian) 

 pulmonary plague cannot spread through the air as the digestive 

 tract is plague-proof, and that direct contact is necessary. 



Lice and Certain Diseases: 



Typhus fever is transmitted from man to man by the Body Louse 

 {Pediculus vestimenti), and Beriberi probably by the Head Louse 



{Pediculiis capitis) . 



Ticks and Certain Fevers: 



Although ticks are not true insects yet they have been considered 

 as coming under the field of the entomologist. In certain western 

 states, viz., Montana, Idaho, Wyoming, Utah and Nevada, the Rocky 

 Mountain Spotted Fever occurs and is produced by the bites of ticks 

 {Dermacentor venustus, et al.) which carry spirochaetes. The African 

 tick-fever is carried by another tick {Ornithodoros moubata), the 

 African Relapsing fever possibly by a tick, the African East Coast 

 fever of cattle by ticks (Rhipicephalus appendiculatus) and the Texan 

 fever of cattle by a tick (Margaropus annulatus) inoculating cattle 

 with the protozoan spirochjete Babesia bovis, a fact observed by Dr. 

 Theobald Smith. 



Other Diseases: 



The terrible "hookworm" disease of the South is probably carried 

 by the common house-fly. The causal organism {Anchylostoma 

 diiodenale) a round worm may also enter the skin from infected soil. 

 Pellagra is transmitted, according to many authorities, by the bites of 

 species of black-fly {Simulium) or by the ingestion of mouldy corn. 

 White grubs (Lachnosterna) are hosts for the thorn-headed worm 

 {Echinorhynchus gigas) and food for swine which in turn becomes 

 food for man. 



Leprosy, that most dreaded disease, is now believed to be trans- 

 mitted by flies, fleas, mosquitoes and bed-bugs. Possibly also certain 

 mites may be occasional carriers of the bacillus {B. leprcs). 



It will be seen from this account that the insects concerned in the 

 transmission of disease are of two kinds: those, like the mosquito which 

 transmit malaria and filiariasis, which are essential hosts of the disease 

 organisms, and those which transmit the disease mechanically. Any 

 insect which habitually attacks man or which may enter the house or 



