i8 



yljV ECONOMIC ENTOMOLOGY. 



a rule, they will bear close watching. One thing is certain, how- 

 ever : no insect with this type of mouth structure can be reached 

 by means of a stomach poison. Destruction through its food is, 



therefore, absolutely impossi- 

 ble, because we cannot poison 

 the plant juices by any method 

 thus far at our command. An 

 insect of this kind is incapable 

 of eating any solid food what- 

 ever, and no matter how thor- 

 oughly covered with a corro- 

 sive poison the outside of our 

 plants may be, it would 'get 

 none, since it only punctures 

 the tissue without absorbing 

 any portion of the outer sur- 

 face. Thus the determination 

 of the type of mouth structure 

 often limits or decides the char- 

 acter of the remedy to be used 

 M i> \1F/ J9 I ^" destroying the insect. 



A '3lJwL^ I Among the Z'/^/ffra, or flies, 



we have a number of interest- 

 the ing modifications of the suck- 

 One series is fur- 

 to 



those in the bugs, but more numerous, representing different 

 mouth structures, and not always carried into the head itself 

 The sucking structure is also quite different, and never forms a 

 rigid, jointed beak. Mosquitoes and horse-flies are examples of 

 this kind ; but gradually the lancets disappear, and in most of the 

 flies only the sucking lip, often greatly and interestingly developed, 

 remains. The common house-flies and blow-flies are types of this 

 modified form, and are capable of taking liquid food only, though 

 often seen attacking solids. If the mouth of a fly be examined 

 under the microscope, there will be seen at the tip of the lip a 

 series of deep grooves, stiffened with chitinous loops, and armed 

 with sharp projecting edges. When the fly wishes to feed on a 

 solid, it scrapes the surface by means of these rasp-like projec- 



Mouth parts of a plant-louse. — a, 

 jointed beak ; (J, the lancets, much enlarged ; ;.,„ rnrjiitj-i 

 c and fif illustrate the feeler and foot. .,,.,, • -i 



nished with lancets similar 



