October, '14] WOLCOTT: ECOLOGY OF TIPHIA 385 



In the late fall a considerable period may elapse after the spinning 

 ■of the cocoon before transformation to pupa«takes place, in fact, pupa- 

 tion may not occur till spring. But if the cocoon is formed early in 

 the fall transformation to adult may be immediate. Indeed, it appears 

 that Tiphia may hibernate either as larva, pupa or adult inside the 

 eocoon. During the summer, however, the cocoon is occupied only 

 a short time betAveen the spring and fall generations. The shed pupal 

 skin contains a considerable amount of a dense white fluid, which later 

 dries in a solid mass. If the adult is active in the cocoon, the pupal 

 skin is ruptured and the dried white mass is ground to a powder which 

 is often seen dusted over the adult Tiphia when newly emerged. Some- 

 times the adult is active before the fluid dries and it presents a sorry 

 spectacle, when the cocoon is cut open, as it crawls out covered with 

 large chunks of the dried fluid adhering. Probably with normal emer- 

 gence the adult is seldom covered with this powder, for many cocoons 

 are found from which the adults have emerged and the pupal skin 

 remains undisturbed and unbroken in the pointed end of the cocoon. 



All my observations indicate that invariably the adults emerge 

 through a hole cut in the side of the cocoon towards the surface of the 

 ground. Usually this is also the larger end of the cocoon, where the 

 head is located, but cocoons have been found with the exit hole cut 

 half Avay, or more, down the side. This condition is not usual, and 

 occurs only in cocoons exposed by the plow. Plowing a field has a 

 most decided effect on the emergence of the adults from the exposed 

 cocoons. Adults which would otherwise hibernate in the cocoon, 

 often emerge late in the fall. Spring plowing may produce an earlier 

 emergence because of the unnatural warmth caused by a few days' 

 exposure to the direct rays of the sun. In 1913, normal emergence 

 was general at Bloomington, 111., on May 14. Indeed, after this date 

 very few cocoons could l)e found from which the adults had not emerged. 

 As grubs parasitized with very small maggots are found as late 

 as the middle of September, the evidence seems to indicate two 

 generations during the year. Plowing is not usual during the summer 

 and it is difficult to tell what the normal subterranean habits of Tiphia 

 are. The adults which prematurely emerge from their cocoons late 

 in the fall appear to perish without ovipositing, as parasitized grubs 

 are never found as late as October 1 as far north as Bloomington and 

 Urbana, 111. Early fall plowing, and indeed fall plowing in general, 

 must be very unfavorable to Tiphia. Even those cocoons which are 

 deep in the ground and are not disturbed by the plow will be somewhat 

 affected, but the majority of cocoons are formed less than six inches 

 from the surface, or in that part of the soil which the grubs normally 

 inhabit during the summer months, and these are exposed to the 



