22 THE HESSIAN FLY IN THE UNITED STATES. 
then it could deposit only on the shoots which develop atthebaseof the 
wheat following the attacks of the preceding generation. A great 
number of the individuals would perish, and the same remark would 
apply for the fourth generation if the month of July and the beginning 
of August are very rainy. In a country presenting the agricultural 
conditions of Vendee a great humidity during the month of July and 
the commencement of August would be unfavorable to the development 
of the Cecidomyia in causing a quantity of individuals to issue which 
would perish for want of suitable food plants. Dryness during the same 
period would, on the contrary, be favorable in permitting the estivation 
of its progeny. 
Quite recently Dr. W. Paspelow, assistant in the zoological cabinet 
of the Agricultural Institute at Moscow, has published a communication 
presenting a number of facts concerning the development of the Hes- 
sian fly, a translation of which, by Mr. C. W. Mally, has been kindly 
furnished me. The following extract contains the points that are of 
interest in this connection : 
The spring generation of the Hessian fly appeared this year in the second half of 
April (old style) and deposited its eggs principally on the young wheat sowings (or 
wheatplants) and in much smaller numbers on the rye sowings (or rye plants). Such 
a selection was only found in connection with the spring generation. 
In the autumn, on the contrary, the rye as well as the wheat fields were attacked by 
the Hessian fly, whereby the early (July) as also the late (August) sowings suffered 
in equal proportions. 
The larvae of the spring generation damaged in the wheat fields 50 per cent, and in 
the rye fields 20 per cent of the stems. 
Toward the end of May the greater portion of the larvae transformed to the pupa- 
rium stage. In the beginning of July the first true pupae were found, and at the 
same time adult flies emerged from pupa 1 kept in a glass. In the first half of June 
a number of the puparia transformed to true pupae ; but the principal portion of the 
Hessian fly (70 to 80 per cent) remained in the puparium stage. Toward the end of 
the same month there were no more true pupae to be found, and during the whole of 
July and the first half of August there were in the field exclusively puparia to be 
found. As an indirect proof of this— that the Hessian fly was retarded in its devel- 
opment — is given the fact that the wheat and rye sown during June for the purpose 
of attracting the Hessian fly remained entirely free, although at the same time they 
suffered greatly from Oscinis frit Fall., and the "ground flea" (Chcetocnema aridella 
Gyll.). From this we can deduce that the emerging of the summer generation, which 
had begun in June, stopped very quickly, so that the same first appeared in the 
autumn — end of August and beginning of September. Such a retardation in the course 
of development of the Hessian fly was due to the high temperature and the great 
drought of the past summer, whereof one could easily be convinced by placing the 
puparia in a moist space — in glasses with damp sand which were placed in moist and 
shady places in the park. In all such cases perfect flies developed in the course of 
two weeks from puparia brought from the field. Puparia left in the field, remained 
on the contrary, in the puparium stage an unusually long time, until in the second 
half of August, under the influence of rain, they transformed first into true pupae and 
after that finally into adult flies. So there were in the past summer only two genera- 
tions of the Hessian fly observed — the spring and the autumn generation.* 
* It is not without interest to remark that, in the room in which the summer puparia 
were kept dry, they remained without change during the course of the whole autumn 
and winter. - 
