29 



tected by trees, until February 28, — the last date on which they 

 were found. All attempts at rearing these unprotected larvae 

 failed, some dying without forming puparia, while others formed 

 puparia that were lighter in color and thinner than the normal 

 form." 



At the present time (November 26) fields near Albion, in White 

 county, are in precisely the condition described above by Mr. 

 Marten, about nine tenths of the flies being naked larvae, and 

 many of them very small. 



The final fate of these hibernating larvse can ouly be determined 

 by observatioDS next spring.* 



[Imagos of the second brood emerging in our breeding cages 

 before harvest, have not ordinarily laid eggs, neither made any 

 apparent preparations for that duty, — a fact which has suggested 

 to me the idea that these midsummer imagos were prepared by 

 nature for an interval of waiting before giving origin to another 

 generation, this interval corresponding to the period of barren 

 stubble fields between harvest and the growth of volunteer grain. 

 However, in one instance, imagos which emerged May 24, 1887, 

 laid eggs at onte in the vials where they were confined, and the 

 occurrence of even four broods of the Hessian fly in Illinois be- 

 comes possible. Confirmation of this supposition is afforded by 

 the occasional finding of puparia Avith living larvae above the upper 

 node of the stem as late as July 12, the eggs for which must 

 have been laid on the upper leaf of the plant, and consequently 

 at a date quite too late for the first or spring generation of ima- 

 gos. June 30, 1887.] 



SUMMARY AND DISCUSSION. 



From all the foregoing we draw the following important practi- 

 cal conclusion, — that the development of a third (autumnal) brood 

 of Hessian-fly larvae derived from imagos which emerge after the 

 first autumnal frosts, may sometimes make of no effect the prac- 

 tice of late sowing — at present the standard defense against the 

 fly — or may even make late wheat more subject to injury than the 

 earlier plantings. How this comes to pass will be seen when it is 

 remembered that late sowing as a defense against the fly is a 

 procedure based upon the delicacy of the winged insect and its 

 sensibility to frosts. By postponement of wheat seeding until the 

 first hard frost of autumn, it is hoped to get beyond the reach of 



"In our breeding cages these hibernating specimens (Edgewood) gave the imago in moderate 

 nnmber from April 23 to May 3, 1887, and the proof of a third brood in our| latitude Is conse- 

 quently complete. 



It must not be forgotten, however, in this connection, that both onr own observations and 

 those of others show that individuals of each generation may lie dormant in the puparium during 

 the whole life of the generation following, finally emerging with the descendants of their original 

 contemporaries. Thos.; i)ui>;iria which I'oriii iu .May nnd June may not yield the imago until Sep- 

 tember; and those which form in volunteer wheat in September may hibernate and emerce in 

 spring. The division into several broods is consequently not complete, and will probably be 

 found less and less so as one passes into more northerly latitudes. 



I suspect that drought may retard the metamorphosis of the larva, and that the generations 

 may follow each other more closely and rapidly in wet weather than in dry. 



