8 



LEAF-MINING INSECTS 



the body becomes cylindric, and when fully extended it 

 tapers forward to the mouth hooks. The mouth hooks are 

 swung with an oscillating motion and shear unopposed like 

 a scythe across a swath. The body rolls; and setulae and 

 fleshy protuberances when present are developed in circles 

 and are effective in any position. 



The larvae of the other three orders differ from this in 

 almost every particular. The body is flat and of a relatively 

 permanent form. It is generally most flattened on the 

 ventral side — the side next the epidermis of the leaf. It is 



Fig. 5. Two sawfly larvae (after Yuasa) . 

 B, an external feeder, Hylotoma spJ 



A, a leaf -miner, Metallus rubi; 



most widened and most strongly chitinized at the anterior 

 end, where flat horny plates both dorsal and ventral cover 

 the prothorax and take the heavy friction against the walls 

 of the mine. Paired jaws are present and they are opposed 

 in action. They work like pincers or shears. The lateral 

 margins of the body become more or less serrate in outline, 

 due to bulging prominences of the middle segments; and 

 ambulatory processes and ambulatory setae are developed 

 in symmetrical bilateral pairs. Details of these adaptations 

 will abundantly appear in the following chapters which treat 

 of the several orders. 



