66 PROCEEDINGS OF THE NATIONAL MUSEUM vol. no 



phase of bilituratus, it might be supposed that during the fairly ex- 

 tensive flights of the 1930's, as reported by Parker, et al. (1955), 

 there would have been signs of spretus development. But such was 

 not the case, and now, in the light of aedeagal characters here dis- 

 cussed, it seems that bilituratus and spretus are distinct species. 

 Nevertheless, for 25 years the view that spretus is the migratory phase 

 of bilituratus [mexicanus] had considerable acceptance (Hebard, 1929, 

 1931, 1936c; Gurney, 1953, p. 314, pi. 7, fig. d; Parker, et al., 1955). 



Brett (1947) felt that settlement of spretus breeding grounds for 

 farming and grazing was responsible in some way for the disappearance 

 of the grasshoppers. Impressed by short-winged specimens reared on 

 alfalfa, he also stressed a possible correlation between the increase in 

 alfalfa acreage and spretus decline. Pfadt (1949, p. 39) expressed 

 doubt that alfalfa was a major factor and implied that the little 

 available information concerning preferred native food plants of 

 spretus is an inadequate basis for any general conclusions explaining 

 the disappearance. We have failed to learn of any pronounced 

 range-plant changes in Montana during the 1860's, 1870's, or 1880's, 

 so far as the general disappearance or replacement of plant species is 

 concerned. (See Andrewartha and Birch (1954, esp. pp. 594-600) 

 for a discussion of conditions related to population fluctuations.) 



The irregular periodicity of historic spretus swarms, the apparently 

 nearly omnivorous appetite and very long-winged condition of 

 swarming adults, and the marching behavior of nymphal bands 

 suggest the occurrence of a migratory phase. If this view is correct, 

 spretus probably had a solitary phase which occurred in relatively 

 localized colonies, possibly adapted to a specialized environment. 

 There is the example of Melanoplus rugglesi, which in the Great Basin 

 attracted widespread attention for about 13 years (1939-1952) as a 

 migratory phase. Previously, rugglesi had been virtually unknown, 

 and at present the solitary phase is scarcely found except by ento- 

 mologists acquainted with the specialized habitat of the small localized 

 colonies. A handicap in studying the possible correlation of weather 

 conditions and spretus abundance is a shortage of reliable weather 

 records, prior to 1886, for such Western States as Montana. 



Griddle (1917) discussed the former prevalence of spretus, and added: 

 "At present, however, the insect seems to have vanished completely. 

 Indeed, there are some who would place it with the Passenger Pigeon 

 as an object of the past. It seems almost incomprehensible, however, 

 that such can be the case. More probably the real permanent 

 breeding grounds are more restricted than was supposed, and the 

 locust will yet be located either by the discovery of its real haunts 

 or by a new invasion following favorable weather conditions for 

 breeding purposes." One immediately wonders whether a solitary 



