65 



stages of the insect can be produced continually from April to October, 

 and by keeping a cage indoors I have produced adults in abundance in 

 January. 



As Br. Lindeman has well stated, the puparia are greatly influenced 

 by environment, temperature, etc., and this is probably true of the other 

 stages, larvae of different ages being, for all we know, influenced to a 

 different degree. To these facts must be added another of considerable 

 moment, viz, while nominally two brooded, flaxseeds collected by me in 

 the spring of one year have lived over to the spring of the following year. 

 This is also true of at least one of the parasites of the species. How far 

 the number of these interlopers is augmented by a retarded develop- 

 ment of greater or less extent it is impossible to say, but that there is an 

 accession through this means there can be no doubt. In fact, it would 

 appear as though nature had in this way provided against the extinc- 

 tion of the species. 



Now, is it proper for us, from these scattering individuals, to attempt 

 to construct distinct broods 1 It seems to me not. I have several times 

 sown wheat at La Fayette early in July and never had it seriously in- 

 fested by Hessian fly until late in August or early in September. Yery 

 young larvae were exceedingly abundant early in October of this year 

 in a field of early- sown wheat near La Fayette. 



It is true that observations during a single season, in a single locality, 

 might produce apparently good evidence of a third brood, but a con- 

 tinued close study of the species in such locality will probably show it 

 unfounded. That these aberrant individuals may, under favorable con- 

 ditions, collect or "bunch" together in certain fields is probably true, 

 but my own experience has been that the following year this irregu- 

 larity will have disappeared or have been reduced to a minimum by the 

 effect of the weather during midsummer and winter. On June 24, 1887, 

 near Princeton, Indiana, latitude 38° 23' N., I found a field of wheat, 

 sown about the first of the preceding November, literally alive with 

 larvae from one-fourth to nearly or quite full grown. There were no 

 pupae to speak of in this field at the time, but in other fields in the 

 vicinity these were abundant, but here there .was no larvae to be found. 

 At this date wheat harvest was at its height. The late-sown field had 

 evidently attracted the late- appearing adults of the fall before, and 

 their progeny, living over in this field, as delayed larvae, emerged cor- 

 respondingly late in the spring, giving rise to the generation of larvae 

 observed by me. My reason for taking this view is that I have several 

 times tried to draw off the spring brood of flies by offering them young 

 plants on which to oviposit, but have always failed, as they seemed to 

 prefer tender shoots of older plants to the young plants themselves. In 

 the fall this characteristic seems to be somewhat the reverse, although 

 even then, if attacked after tillering, the tillers will be chosen instead 

 of the main stem. The fall brood of adults is probably the migratory 

 brood, and their power of detecting wheat plants is almost phenomenal. 

 25910— Bull. 23 5 



