October, '16] MCGREGOR- BUCCULATRIX THURBERIELLA 507 



and epidermis remain (PL 37, fig. 4). Small, ill-nourished plants are 

 usually killed, while larger plants are often seyerely injured. Occasion- 

 ally larvae feed upon the calyx and involucral bracts which results 

 usually in the shedding of the form. On account of the thickly honey- 

 combed nature of the leaf lesions, which is so characteristic of 

 Bucculatrix-infested cotton, we propose as a common name for this 

 species the "cotton leaf-perforator." 



Life-History 



The Egg. — The egg is very small, being barely discernible to the naked e3'e. It is 

 projectile-shaped, pale straw-color, with about ten longitudinal ridges and inter- 

 vening grooves, giving it a strongly fluted appearance. In addition to this, a reticu- 

 late system of smoky-colored mottlings decorate the surface. The egg is placed 

 upright on the leaf, standing on its largest end. No prefei-ence seems to be shown in 

 ovipositing as between the top and under sides of the leaf. Since we have been un- 

 able to induce egg-laying under control, it is impossible to present data as to the 

 duration of the incubation period. Eggs in out-of-door locations on a few occasions 

 have been observed 24 hours prior to hatching which indicates that the period is some- 

 what in excess of that interval. 



The Larva. — First Instar. — ^Upon hatching the larva bores into the leaf directly 

 at the point of attachment of the egg and begins to tunnel. The mine lies nearer 

 the upper surface than the lower, and progresses tortuously, ever widening in calibre. 

 The average total length of the tuimel, as determined from a measured series, is about 

 one inch. When this instar is about completed an exit hole is cut through the upper 

 epidermis, and the larva deserts for all time the inner tissue. Upon coming to the 

 exterior the first instar individual occasionally feeds for a brief period on the upper 

 leaf tissue. The time required for the completion of this instar is about three days. 



When the feeding activities of this stage are finished the larva weaves a tiny cir- 

 cular web over some slight depression on the under side of the leaf into which it re- 

 pairs for the first molt. The initial molting web consists of two fabrics, first a "fly" 

 web of loose texture is woven and under this is spun the more compact fabric. A 

 somewhat concealed aperture is left through which the individual makes its exit 

 after molting. A large series of these primary molting webs averaged Vis inch in 

 diameter. The molting period covers about twenty-four hours. 



Second Instar. — Upon the appearance on the leaf of the second larval instar, feed- 

 ing at once begins. This may take place on either the upper or the under surface. 

 The leaf tissue is devoured only to the opposite epidermis, but the remaining tissue 

 often collapses, thus forming irregular-shaped lesions (see PI. 36, fig. 2). After 

 about 1.5 days at El Centro, the larva selects a concavity, normally on the under sur- 

 face between two large veins, and spins the second molting cocoon. These are similar 

 to the primary cocx)ons but are larger, averaging about ^ /s2 inch in diameter. The 

 larva lies in a looped position — head to tail. The quiescent period is determined 

 from our data to be 1.1 days. 



Third Instar. — At the conclusion of the second molt the larva of the third instar 

 emerges and at once begins to feed in a manner similar to individuals of the second 

 instar. This is the most aggressive stage and the one causing the greatest amount of 

 injury to the cotton leaf. As a rule, not more than two or three larvaj occur on a 

 single leaf, but occasionally as many as a half dozen have been seen. The last act 

 of the third larval instar individual, after the completion of the pupal cocoon, is the 

 shedding of the larval skin which occupies a position within the cocoon just behind 



