Observations on the Life History of Taphrocerus gracilis 7 



the pupae, are to be found. The exact length of each instar has not been 

 determined. It seems probable that the instars vary, for larvae of the 

 different instars have been found at widely different times and in burrows 

 of various lengths. The length of the larval stage varies from about three 

 to four or more weeks, and the greatest amount of the mining is done during 

 the last three or four days of feeding, as is shown by the measurements 

 given in a preceding paragraph. 



When the feeding has ceased, the larva measures seven or eight milli- 

 meters in length and appears rather plump. At this time it crawls to the 

 more spacious central part of the mine, where, surrounded by an accumu- 

 lation of dried pellets of excrement, it undergoes metamorphosis. 



The pupa 



The pupa as it first emerges from the larval skin, is soft and white. In the 

 course of a few hours, the outer covering becomes hard and brown. In the 

 laboratory this was observed to take place within about twelve hours, and 

 field observations indicate that this is, about the average length of time. 

 No motion has ever been observed in the pupa from shortly after the 

 time that it emerged from the larval skin until the emergence of the adult. 

 Under laboratory conditions the pupal stage lasts ten days, which probably 

 is a fair representation of the normal. 



In order to permit the emergence of the adult, the pupal skin breaks 

 along the median line from the anterior margin of the prosternum, on the 

 ventral side, over the head and prothorax to the anterior margin of the 

 mesotergum. As the adult appendages are drawn out, the chitinous 

 covering of the pupa ruptures along the impressed lines which outline the 

 wings and legs and the thoracic segments, making the emergence of the 

 adult less difficult. 



The adult beetle 



Within a few days after emergence (which at Ithaca, New York, takes 

 place about the second week in August), the adult beetles start feeding on 

 the tender top shoots of the flood-plain bulrush. On warm, sunny clays 

 they may be seen feeding on the edges of the leaves, cutting little notches 

 which are sometimes so deep that they cause the leaves to bend over. 

 The beetles fly very rapidly, but they seldom seem to have occasion to 

 fly about; several beetles have been observed to remain feeding on the 

 same plant for more than two hours. Much of the time they walk about 

 examining the edges of the leaves, apparently to no purpose. 



They often continue to feed on warm autumn days even after the first 

 frosts, which do not seriously injure the bulrush. At Ithaca in 1915 

 the beetles were abundant as late as October 14. In 1916, at the Univer- 

 sity of Minnesota, two beetles remained on bulrushes in a cage until 

 October 5. 



The hibernation of the beetles is as yet an unsolved problem. From 

 the time of their disappearance from the leaves of the bulrush in the fall 

 until they reappear on the new leaves in the spring, no trace of them has 

 been found. The fact that the beetles have never been found in any 

 part of the plants late in the fall or during the winter, together with the 

 fact that the areas on which Scirpus fluviatilis grows are completely 



