THE DIPTEROUS PARASITES OF ALETIA. 109 



the larvse of Pliora, some tlie larva of this Cyrtoneura, while the largest portion con- 

 tain only a badly smelling lluid. If further observations prove that this fly infests 

 only such chrysalides and cannot bo bred from the living Aletia larva, it cannot be 

 considered a true parasite. — C. V. Rilerj. 



The Taohina Flies. — The other Dipterous flies belon*^- to the genus 

 Tachina. The first of these was described by us in the Canadian En- 

 tomologist, 1879 (Vol. XI, p. 162) as Tachina aleticv,^^ and is the most 

 abundant Dipterous enemy of Aletia. It measures about one-third of 

 an inch in length, and is more robust and slightly larger than the com- 

 mon house-fly, from which, as well as from the Sarcopliaga (which is 

 less robust than the Tachina)^ it may be distinguished by having the 

 bristle of the antennae smooth and not hairy. These Tachina flies are 

 more completely parasitic than the flesh-fly above mentioned, and their 

 eggs are harder, more polished, and very firml^^ attached to the worm, 

 usually just behind the head, where they cannot be molested. The 



larvae or maggots have the same habits and 

 mode of transformation as those of Sarcophagaj 

 and the accomiDanying figure (Fig. 38) of Ta- 

 china Jfavicaiida Eiley, will serve to illustrate 

 the flies. Occasionally these maggots are not 

 full fed, and do not destroy the Aletia till 

 after it has assumed the chrysalis state, but 

 ordinarily they issue from the worm itself, 

 which is frequently infested by more than 

 Fig. 38.— Teiiow-taiied Taciiina-fly. ouc. The spccics was reared from chrysalides 

 ^^' sent by Mr. Grote from Savannah and by others 



from various parts of the South, including the States of Alabama, Mis- 

 sissippi, and Texas. 



Another species of Tachina has been described by Professor Comstock 

 (Annual Eeport of Commissioner of Agriculture, 1879, p. 303)^^ as T. fra- 

 terna, resembling T. aletice quite closely, but found to differ upon careful 

 examination. 



The number of worms killed by these Tachinid flies is very hard to es- 

 timate. Their eggs are very common on the backs of the cotton cater- 

 pillars, especially towards the end of the season, occasionally as many 

 as 8 or 10 eggs being found upon a single worm. Observers have esti- 

 mated at different times the proportion of worms thus parasited, and it 

 has occasionally reached as high as 40 -per cent. ; but all who have ob- 

 served these parasites at all have been struck by the fact, in the first 

 place, that a very large number of the eggs are discarded with the cast- 

 off skins at molting, and so the larvae which hatch die for want of sus- 

 tenance, and, in the second place, that the Tachinid larvae destroy oue 

 another quite as readily as they feed upon the caterpillars. It is true 

 that Mr. Trelease has recorded an instance in which a skin was shed 

 without removing an egg, but this we must regard as exceptional. The 



