HOW TO KNOW THE IMMATURE INSECTS 



3a. Head incomplete; thorax and abdomen combined consisting of 13 

 segments; larvae peripneustic; usually with a sclerotized plate on 

 ventral surface of mesothorax. Fig. 535. ..Family CECIDOMYIDAE 



The larvae ore mostly gall-mak- 

 ers, but some are predacious on 

 scale-insects and others live in 

 decaying organic matter. The 

 Hessian fly, Phytophaga destruc- 

 tor (Say) is a serious pest of 

 wheat. The larvae live and feed 

 on the stem beneath the leaf 

 sheaths, where pupation also takes 

 place. 



Fig. 555. Retinodiplosis inops O. S. 



3b. Not so 4 



4a. Head and thorax and 1st and 2nd abdominal segments fused; 

 larvae with minute abdominal spiracles; abdomen with a ventral 

 longitudinal series of sucker-like discs. 

 Fig. 536 Family BLEPHAROCERATIDAE 



The adults are called net-winged midges. The lar- 

 vae live in swift-flowing streams and feed on algae 

 and diatoms. They may be found clinging to the 

 rocks. Pupation takes place in the water. 



Fig. 536. Bibio- 

 cephala sp. 



4b. Head free, or if retracted within or fused with prothorox the other 

 thoracic segments are distinct 5 



5a. Head complete; mandibles opposed. 



190 



