ENTOMOLOGY 209 



They appear early in May and at once begin laying eggs for an- 

 other generation, which passes through the same stages from egg to 

 adult as the first brood, the history of which has just been outlined, 

 except that less time to produce a generation is required as the 

 weather grows warmer. During the season therefore, there is time 

 for eight or nine generations to complete their life histories, each 

 year. As fall approaches, however, fewer winged adults appear, 

 more wingless ones being produced, until in October only about 

 2 per cent are winged. Egg-laying by the last generation of adults 

 may continue until snow comes, but only the adults appear to be 

 able to survive the winter. 



The amount of injury done by these minute insects is little ap- 

 preciated on account of their small size, but what they lack in this 

 regard is made up by their numbers. It has also been noted that 

 while the increase appears to be extremely rapid during the early 

 summer months, the heavy showers of midsummer appear to destroy 

 many of the insects. 



The adults of this species feed entirely upon the leaves and 

 external parts of the grass. They are very seldom found within 

 the sheath of a leaf, but frequently congregate in numbers within 

 the terminal leaf before it has fully unrolled. They select the 

 fresh tender parts of the grass, and consequently their work is most 

 apparent upon the upper leaves. The mouth parts are used to pierce 

 the surface of the leaf and the wall of a cell below. As soon as the 

 juices contained in this cell have been extracted, the piercing mouth 

 parts are withdrawn and another cell is punctured, the empty cells 

 presenting a shrunken, whitish appearance. The insects usually 

 feed lengthwise of the leaves, their path being marked by whitish 

 streaks in the tissue of the leaf and by dots of dark excrementitious 

 matter. 



The young seek a more protected place in which to feed, and 

 may be found in large numbers within nearly every sheath of June 

 grass during the latter part of May and through June. A favorite 

 haunt is in the head, just as it is making its appearance. The 

 minute young work their way down inside the sheath, and some of 

 them, reaching a node where they must stop, continue to feed upon 

 the juices from the very tender stem within until shortly before 

 they enter the pupal stage. The young may be found within any 

 sheath ; but it is almost always those that enter the top sheath which 

 cause the silver-top, as these directly cut off the supply of sap to the 

 head. Examination of affected stems shows that at a point just 

 above the upper node the stem has been sucked dry for about half 

 an inch of its length. 



This minute pest attacks a number of species of grass, but by 

 far the greatest damage is done to June grass, few fields of this es- 

 caping more or less serious injury. After the first of July, by which 

 time June grass has usually matured, the insect changes to some 

 later species, as timothy when this is present. They may _bo found 

 in abundance upon barn-vard grass from mid-summer till late in 

 the fall, 



