452 JOURNAL OF ECONOMIC ENTOMOLOGY [\"ol. 7 



The tortuous courses of the burrows occasionally sever the veins of 

 the leaves, causing the death of more or less of the leaf tissue. It 

 rarely happens, however, that one tunnel intersects another. 



As the grub increases in size the caliber of the burrow expands 

 (plate 14, fig. 1) until full development is attained at its cavernous end. 

 Having reached maturity, the larva deserts the leaf dorsall}' through 

 a somewhat crescent-shaped incision (plate 14, fig. 5) near the large 

 end of the mine. Measurements of a series of these exit holes averaged 

 1.00 mm. for the longest axis and .42 mm. for the shortest axis. The- 

 average dimensions of a number of mature larvse in natural position 

 (unextended) were 2.00 mm. long by .55 mm. thick. Since the act 

 of egg-laying has never been witnessed by the writer, it is impossible 

 to record with exactness the duration of the larval stage at Batesburg. 

 However, a series of twenty-three larvse collected in ver}^ new mines 

 averaged about four days to pupation. Probably about one or two 

 days had been spent by these larvae in developing the mines to the 

 point reached at the time of collection. This would fix the duration 

 of the larval stage in cotton at Batesburg at about five or six days, 

 which is somewhat greater than that established by Webster and Parks 

 for this stage. 



Pupa 



In the great majority of cases observed, the mature larva, upon 

 escaping, sought the soil at the base of the stock for pupation. Usuallj'" 

 the larva buries itself very shallowly — not much more than covering 

 itself. In a few cases pupation has occurred on the under surface 

 of the leaf from which the individual emerged. These are marked 

 exceptions, however. In no case have we ever known a miner to 

 pupate within the mine. The puparium at first is a pale straw- 

 color but as normal development takes place the color deepens to a 

 golden-tan. In the case of parasitism the puparium changes in color 

 to a smokj^-brown. 



A rather large series of measured pupse averaged 1.62 mm. long by 

 .72 mm. wide. Data is at hand covering development from the 

 immature larva to adult for sixty-seven individuals. We find that 

 for Batesburg, S. C, the pupal period for May, June and July ranges 

 between six and twelve da3^s as extremes. The weighted average 

 for all individual cases gives 8.67 days as the normal pupal period 

 for summer temperatures. 



The fly issues from the puparium through a rupture at one end. 

 The only adults actually observed in the act of emergence liberated 

 themselves in the morning between the hours of 8 and 9 o'clock. 

 As previously stated, several attempts have been made to induce 

 oviposition under control. Potted cotton seedlings were placed 



