270 THE PRACTICAL APPLICATION OF ECOLOGY 



internode below it. A typical attack, at this period, shows a stem 

 with two or three internodes, terminated by a swollen region, 

 consisting of the ear enclosed by its ensheathing leaves, from 

 which it never escapes, and therefore cannot ripen. A striking 

 feature in the behaviour of the insect is its instinct always to bore 

 downwards. Should the fly deposit its egg upon a leaf, whose base 



Fig. 74. Diagram of barley shoots, showing C, " critical " leaves ; 

 |C, "half critical" leaves; E, ear; and NC, "non-critical" 

 leaves. (After Frew.) 



comes off from the shoot helow the ear, the newly hatched larva 

 cannot reach the ear to feed ; such leaves may be termed 

 " non-critical leaves." In thirty-six instances dead larvai were 

 discovered by Frew in the ear-bearing internodes, and in all cases 

 the ear had remained untouched. In these examples the young 

 larvae entered the shoots below the ear, and, owing to the toughness 

 of the tissue and lack of suitable nourishment, they had perished. 

 If, on the other hand, an egg is laid on a leaf which arises from the 

 shoot above the base of the ear, the ensuing larva, by migrating 



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