240 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



survives to propagate when hatching out the same season, or whether 

 auy but those which reach sufficiently northern latitudes to insure the 

 keeping of the eggs through the winter, are instrumental in perpetuating 

 the species. 



In a year like 1875, when vast and heavy swarms succeed in reaching 

 the Permanent region, they no doubt lay eggs, and their issue the follow- 

 ing year is very apt to invade the fertile country again, especially if, as 

 was the case in 1876, they are joined by others whose parents had 

 hatched the previous year in said Permanent region. In a year like 

 1877 (and that of 1867 was very similar), comparatively few of the de- 

 parting insects got back to breed, the great bulk of them perishing on 

 the way. i 



DO DEPARTINGr SWARMS FROM THE TEMPORARY REGrlON ETER RE- 

 TRACE THEIR COURSE? 



This is a question more difficult to answer, but which must be an- 

 swered, from present knowledge, in the negative at least for those 

 which depart from south of the 42d parallel. A few scattering in- 

 dividuals were observed passing southward in Missouri, Kansas, and 

 Texas, in the autumn of 1875, and while their small size and dark color 

 indicated that they had not come from the far northwest, the lateness 

 of the season precluded their being the same individuals which in early 

 summer had flown from the same States. There are, in fact, good rea- 

 sons why all those which breed south of latitude 42^ should not return 

 after once leaving the country in which they hatchf ^ Those of them 

 which do not perish will have laid their eggs before the winds set in to 

 the southeast, and should they return to oviposit wh^re they developed 

 the eggs would prematurely hatch and the second generation of young 

 perish. This reasoning applies with less and less force as we go north 

 and west, or, in other words, as we approach the permanent region, and 

 the probability is that in what we have termed the Subpermanent region 

 many of the insects which depart toward the north, subsequently re- 

 trace their course. The records seem to indicate that such was the case 

 in 1877, and the autumn flights which we have reported (App. 12) were, 

 in all probability, composed of insects reared in said subpermanent 

 country ; for they were neither as disastrous, as injurious, nor as fecund 

 as those which in previous years have come from the farther northwest. 



THE SPECIES IS ESSENTIALLY SINaLE-BROODED. 



Some writers, and notably Mr. G. M. Dodge, of Glencoe, Dodge 

 County, Nebraska, have strenuously advocated the belief that the Kocky 

 Mountain locust produces two generations annually, and as it is our 

 desire to get at the facts in such a case, since they have an important 

 bearing on the general problem, we present Mr. Dodge's arguments as 

 the strongest that can be made in favor of such a view ; for he has had 



3'=» Mr. Tliotnas disspnts from this co'^cliision, believing that swarms often retrace their qourse, even 

 wbeu departing from S. of the 42d parallel. 



