CHAPTER . IV. 

 THE DISEASES OE GEAMINEOUS CEOPS. 



(1) The Parasites of Barley (Hordeum distichum). 



The Grain Aphis (Aphis granaria, Siphonophora 

 granaria) is about the same size and somewliat like the 

 bean aphis already described. The abdomen of the winged 

 female is green, the thorax and head brown, and the 

 wings green with brown veins. The wingless female 

 (viviparous) has a greenish coloured body with brown 

 antennse, and the legs are devoid of hairs. Both the wing- 

 less and winged females have red eyes. The pupae are 

 of a chrome-yeUow colour and the larvae green. A. 

 granaria injures oats, rye, and wheat, as well as barley, 

 by sucking the juices from the young stems and leaves of 

 these crops. Later in the season, this insect attacks the 

 ears of com (when the grain is green), and often causes 

 considerable damage. On the authority of Mr. Walker, 

 Aphis granaria passes the winter on " certain grasses." 



Prevention. — (1) The Grain Aphis has two parasitic 

 foes, namely — Ephedrus plagiator and Aphidius avence — 

 two flies (about the same size as Aphis granaria) belong- 

 ing to the Ichneumonidce. These flies pierce the bodies 

 of the aphides with their sharp ovipositors and lay an egg 

 in each newly-made cavity. The eggs soon turn to larvae 

 which feed on the aphides. These parasitic flies remain 

 within the bodies of the aphides during the pupal stage, 



77 



