222 Bulletin 308 



The cocooit. — When full grown the larva leaves the mine through a 

 cut in the upper surface of the leaf, falls to the ground, and there constructs 

 a small flattened browTiish cocoon in cracks in the soil, under loose stones, 

 or between the base of the tree and the surrounding soil. Where the 

 ground is undisturbed, the cocoons are rarely found more than an inch 

 below the surface. Sod furnishes ideal winter quarters for the cocoons. In 

 Fig. 26 is shown the method of cultivation formerly followed in the Hooker 

 orchard; the space between the rows was thoroughly cultivated, but a 

 strip of sod several feet in width left beneath the trees afitorded excellent 

 winter quarters for the cocoons, and was probably an important factor 

 in producing the very hea^'y infestation of the orchard. The cocoon 

 (Fig. 29) is Hght brownish in color, broadly oval, and moderately arched; 

 it is about 2^ mm. long by i^ to 2 mm. wide, and is usually slightly wider 

 at one end. It is surrounded by a thin flange formed by the closely united 

 edges of the tvro valves of which the cocoon is composed. The cocoons 

 are held in place by a few strands of silk. The time at which the larvae 

 become mature and construct their cocoons varies considerably with the 

 season. On Jiily 6, 191 1, about one half the larvae had left the mines; 

 on Jtily 21, 1908, and July 19, 1909, a few larvae were still present in the 

 mines. 



The pupa. — After forming the cocoon the larva apparently does not 

 transform at once; a cocoon opened August 4, 1908, contained a lar\-a. 

 The winter, however, is passed in the pupal stage. On October 10, 191 1, 

 the writer opened a number of freshly gathered cocoons and found that 

 all the larvs had transformed to pupae. 



The pupa (Figs. 30, 31, and 34) is about 2 mm. in length, ovate pointed 

 behind, and somewhat flattened. The ventral siirface is brownish yellow, 

 the dorsum greenish. The eyes are dark colored and the orange tuft on 

 the head of the moth shows through the pupal skin. On the dorsimi of 

 the abdomen there are six transverse interrupted rows of short brownish 

 spines. On each side of the dorsum is a longitudinal row of wart-like 

 protuberances, each bearing a colorless spine. The anterior spines are 

 very short and they gradually increase in length toward the tip of the 

 body. When about to transform to the adult the pupa works itself partly 

 out of the end of the cocoon, probably by the aid of these spines. The 

 empty pupa skin is left protruding from the cocoon. 



PARASITES 



No parasites were observed infesting the plum leaf -miner until May 

 II, 191 1, when a cocoon was found containing the larva of a Chalcis-fly. 

 The lar\-a (Fig. 37) is 1.4 mm. long, smooth, whitish in color, and rounded 

 at both ends. On June 2, 191 1, two adults of the parasite were found 



