-Larva of Hessian-fly, feeding above 

 a knot, magnified. 



134 INJURIOUS AND OTHER INSECTS 



larval skin bursts open, and the pupa is exposed; shortly 

 afterwards the pupal skin also is cast, and the fly escapes, 

 to lay the eggs from which a new generation will proceed. 



The eggs are minute, 

 and of red colour. 

 One, two, or three are 

 usually laid upon one 

 plant. As soon as 

 the larva becomes free 

 it creeps down the 

 stem to the next joint, 

 which is near the ground. It makes its way between the 

 haulm and the sheath (which is also the base of a leaf), 

 and here it begins to suck the sweet, nutritive juices of the 

 plant. More than one larva may be found feeding at the 

 same joint. The loss of sap causes the plant to flag. The 

 haulm bends sharply just above the joint affected, and the 

 growth of the ear is checked. The young larva is soft, 

 white, and footless, with a minute, retractile head. The body 

 tapers both in front and behind. Nearly all the segments 

 bear spiracles, except the two which in the fly support the 

 wings and halteres. On the under side of the prothorax is 

 a hard scale, divided into two forward-pointing prongs. A 

 larva taken in the act of feeding shows a green line running 

 along the centre of the body ; this is the digestive tube, 

 filled with a greenish sap, sucked out of the plant. Four 

 weeks after hatching the grub is of full size, and about 

 6 mm. (^ inch) long ; 

 the original white col- 

 our has now changed 

 to yellow. It ceases 

 to feed, retracts its 

 head, and changes to 

 a seed - like object, 

 pointed at each end. 

 The larval skin is not 

 cast, but becomes coated over with a fluid exudation from 

 the body, which hardens on exposure to the air, and forms 

 a protective husk or puparium of chestnut -brown colour. 

 In this condition the insects are called " flax-seeds." Not 

 only the Hessian-fly, but all the insects of the same genus 



Fig- 7A-- 



' Flax-seed," or pupa of Hessian-fly, 

 magnified. 



