Mar. i, 1921 Biology of the Smartweed Borer 843 



It will be noted that in Table II only live instars are listed, but that 

 the fourth is nearly equal to the combined length of the fourth and fifth 

 of Table I. It is possible that an error has been made here, but the notes 

 are clear. The matter will be reviewed another year. 



Chittenden mentions 11 and 17 days, respectively, as the lengths of 

 the pupal stage of two specimens reared by him from cornstalks from 

 Kansas. 



NATURAL CONTROL 



The smartweed borer varies greatly in abundance from year to year, 

 and this seems to be due, in Tennessee at least, to variation in the abun- 

 dance of its parasites. Here the most important of these appears to be 

 (Panzeria) Pyraustomyia penitalis Coq., as over 40 per cent of the larvae 

 taken in the field at Knoxville for rearing were killed by it. Chittenden 

 notes that this same species also killed more than 50 per cent of the 

 larvae taken by him in raspberry stems. The host grows normally and 

 reaches its final instar before the maggot emerges. In its last instar 

 the host becomes sickly and inactive, paler than normal, and finally 

 incloses itself in a loose webbing. The parasite maggot emerges and 

 pupates beside or partly within the remains of its host, often closely 

 crowded into the cavity with them. In the overwintering larvae the 

 parasite remains within its host's body until spring and about the middle 

 of May emerges and pupates in the normal manner. The pupal period 

 for the fly varies from 13 to 16 days, being more often the latter. The 

 flies that have been reared by the authors have emerged during two 

 distinct periods — May 30 to June 10 and August 18 to September 12 — 

 coinciding closely with the normal dates for the emergence of the moths. 

 This leads to the assumption that the flies must attack the host larvae 

 during their early instars. 



Coquillett (2, p. 15, 17, 19, 27) records three other tachinid flies (two 

 of them quoted from Townsend (9, p. 467) ) as reared from " Pyrausta 

 penitalis" — namely, Exorista vulgaris Fall., Hypostena variabilis Coq., and 

 Phorocera comstocki Will., but the information given is not sufficient to 

 determine whether they are parasites of Pyrausta ainsliei or of the true 

 Pyrausta penitalis. 



Cremastus facilis (Cresson) was reared by Chittenden. 



Three apparently distinct hymenopterous parasites have been found 

 by the writers. One of these had* spun a white cocoon and attached it 

 to the remains of a host larva in its burrow. The second species was 

 represented by small grubs which filled a dead larva. These grubs later 

 made gray cocoons, only one of which developed. Two grubs of the 

 third species were found attached externally to a larva. One of the 

 grubs developed to an adult and was determined by Gahan as Micro- 

 bracon sp., a male, and not specifically determinable. The authors 

 have not received determinations of the other material. 



