INSECTS AND DISEASE 7 



attracted to the food of human beings, and introduce thereon 

 the pathogenic organisms from their mouthparts and feet. 



The actual measures of control are quite often dependent on a 

 knowledge of the mouthparts of the insect concerned. 



Inadequacy of old systems. In the study of Medical Ento- 

 mology it is no longer sufficient to divide the insects into only 

 two groups as based on the mouthparts, namely, Mandibulate, 

 or biting, and Haustellate, or sucking. This fact becomes 

 clearer when it is considered that the housefly (Musca domestica) 

 and the stablefly (Stomoxys calcitrans) both have sucking 

 mouthparts and belong to the same family, Muscidae, hence 

 are systematically very closely related, yet from the standpoint 

 of disease transmission are widely different. By virtue of the 

 piercing structures composing the mouthparts of the stablefly it 

 relates to direct infection, while the housefly's proboscis, quite 

 ineffective as a piercing structure, relates it to indirect infection, 

 not however of less importance as a disease transmitter. 



Because of the deficiency of the older systems of mouthpart 

 classification the following types will be considered. 



Types of insect mouthparts. The following types of mouth- 

 parts may be recognized: 



1. Orthopteron type, biting or chewing structures, as in the 

 grasshopper. 



2. Physopodan type, transitional mouthparts of biting form 

 but functionally serving as suctorial organs, as in the thrips. 



3. Eemipteron type, suctorial organs enclosing three or four 

 piercing setae closely ensheathed within the labiurn, as in the 

 cone-noses. 



4. Dipteron type, suctorial organs; no special example being 

 available for the entire order, the following subtypes must be 

 recognized: 



A. First subtype Mosquito, loosely ensheathed piercing 

 bristle-like structures, six in number. 



B. Second subtype Horsefly, piercing blade-like structures, 

 six in number, loosely ensheathed. 



