STRUCTURE AND DEVELOPMENT OF INSECTS 



25 



Biting Mouth-parts. Mouth-parts typical of those of biting 

 insects are ca.sily seen in the grasshopper (Figs. 17 and 18). In 

 brief, they consist of an upper and a lower lip, between which 

 are two pairs of jaws which work transversely. The upper pair 

 of jaws, or mandibles, are stout, short, and horny, usually sharp- 

 ened at the tip, slightly serrated at the margins, and flattened at 

 the base. The lower pair of jaws, or maxilla?, arc longer, not so 

 strong, and to each of them is attached an accessory lobe, and a 

 jointed style called a palpus or feeler. At each side of the lower 

 lip is another palpus, these palpi bearing sensory organs. 



Sucking Mouth-parts. In the sucking insects these mouth- 

 parts arc prolonged into a tube through which the juices of the 

 food plant or animal are sucked. In the plant-lice and other 



FIG. 18. A, mouth-parts 

 of grasshopper sep- 

 arated to show posi- 

 tion and relation; B, 

 mouth-parts dissected; 

 Ibr., labrum; md., man- 

 dible; hyp., hypopha- 

 rynx or tongue; TUX. p., 

 maxillary palpus; Ib p , 

 labial palpus; lab., lah- 

 ium; max., maxilla*. 



bugs the lower lip is elongated so that it forms a tube, and the 

 maxillae and mandibles consist ot long hair-like bristles, or setse, 

 enclosed within this tube (Fig. 20). The tip of this beak is rested 

 upon the surface of a leaf into which the setse are thrust, lacerat- 

 ing the tissue, and by a pumping process of the mouth the 

 juices are sucked up through the beak. The structure of the 

 mouth-parts of the various orders of sucking insects varies con- 

 siderably, but all agree in that they suck up the food in a liquid 

 state. Any application ot a poisonous spray to the surface of 

 tohage will be of no avail against them,* though sure death to 



* Liquid poisoned baits, used for house-flies, adults of onion-maggots, etc., 

 form an exception to this rule. 



