THE SPIKE-HORNED LEAF-MINER. 9 



localities of southern ' Calif ornia. The larva, hatching from an egg 

 deposited near the tip of the leaf blade, begins burrowing between the 

 upper and lower epidermal layers of the leaf. 



During its first day in that stage it makes a burrow from 5 to 17 

 mm. in length, directed toward the base of the leaf. After two or 

 three days of burrowing it frequently pursues a zigzag course within 

 the leaf, thereby cutting off the sap supply. In the course of about 

 four days the length of the burrow may reach from 4 to 6 inches. 

 The larvae soon enter the leaf sheath and in small tender plants 

 burrow into the center of the stem, killing that particular stool or the 

 entire plant. 



Up to the present time this species has never been recorded as a 

 serious pest of agricultural crops. The most severely infested field 

 observed by the junior author was one of barley at Yuma, Ariz., on 

 April 16, 1915, in which about 5 per cent of the plants had one or 

 more of the leaves mined by larvse of Cerodonta. 



At Tulare, Cal., both wheat and barley fields showed that about 2 

 per cent of the plants were infested by this species on May 16, 1914. 



In older plants, with more leaf surface and less tender stems, the 

 larvae, after reaching the base of the leaf, will not enter the stems, but 

 proceed down the sheath. The hearts of such plants are not injured, 

 and consequently the damage inflicted is very small in comparison 

 with that upon young tender plants. However, if a plant has a num- 

 ber of larvae mining in the leaves, considerable injury may be done. 

 The mines traversing the leaves from tip to base (PL II, fig. 4), from 

 one side to the other, have a tendency to interfere with the sap flow 

 of the leaves, which eventually turn yellow and die. In long leaves, 

 such as those of older corn plants, the mines in the leaves frequently 

 reach from 15 to 20 inches in length before the larva is fully de- 

 veloped. 



LIFE HISTORY. 



OVIPOSITION. 



The act of oviposition has been observed upon the leaves of millet 

 by the senior author at Columbia, S. C. ; upon wheat by Wildermuth, 

 at Tempe, Ariz. ; and upon barley by the junior author at Glendale, 

 Cal. The general method of oviposition is very similar on these three 

 different food plants. 



The female fly selects a suitable place for oviposition, usually near 

 the tip of the leaf or along the edge. With head elevated and tip of 

 abdomen lowered, the body is held almost perpendicular to the leaf 

 surface, and by rapid piercing movements of the abdomen the epi- 

 dermal leaf tissue is punctured. The ovipositor is then forced by 

 repeated thrusts to its full length between the upper and lower layers 

 of the leaf, the egg quickly deposited, and the ovipositor withdrawn 

 56323°— Bull. 432—16 2 



