

18 BULLETIN 424. U. S. DEPARTMENT OF AGRICULTURE. 



HIBERNATION. 



According to earlier records by Edwards and those a little later 

 by Scudder, which treat of the species in its northern rather than 

 in its southern range, the alfalfa caterpillar hibernates as larvae and 

 adults, whereas G. H. French, 1 in his revised edition of Butterflies 

 of Eastern United States, reports the species as hibernating as 

 chrysalids. The writer has observed the species hibernating in all 

 three forms, if it could really at all times be termed hibernation. 

 Hibernating chrysalids were found upon weed and alfalfa stems by 

 the writer at both Tempe, Ariz., and El Centro, Cal., and at Welling- 

 ton, Kans., Mr. Kelly reported the finding of hibernating pupae be- 

 neath fence rails. Just a few larvae have been collected by sweeping 

 at various times during the winter season at Tempe. During the 

 last week in January, 1912, a single larva was taken, while in Janu- 

 ary, 1913, Mr. It. N. Wilson took a third-instar larva less than two 

 weeks after a very severe cold spell, i. e., severe for the Salt River 

 Valley, a temperature of 13° F. having been recorded on two suc- 

 cessive nights. On warm days adults have been observed in flight 

 several times during the winters when the species was under obser- 

 vation. In 1910 adults were taken at Tempe early in December, and 

 Mr. W. E. Packard took them during the third week in December at 

 El Centro, Cal. In the winter of 1911-12 adults were seen on the 

 20th of December and again in the middle of January. Larvae have 

 been collected in January and, pupating within a few weeks, have 

 issued early in March. Pupae collected in December have issued in 

 February, but adults have never been noted to deposit eggs during 

 the month of January. It is thus seen that at times hibernation 

 amounts to nothing but a prolongation of one of the three stages, 

 the usual activity for each respective stage being resumed on warm 

 days that occur during the hibernation period. 



According to Boll 2 the species aestivates in Texas as larvae during 

 the dry period in summer when the food supply has become ex- 

 hausted. The writer has never witnessed the aestivation of this spe- 

 cies in the Southwest. In fact, it has always occurred in most 

 abundance during the hotest months of the year, notably July and 

 August. Other bureau records likewise show no report of aestiva- 

 tion. It seems safe to assume that the change in habit from that 

 early reported by Boll in Texas is due to recent irrigation of tracts 

 of land well distributed over the arid regions of the Southwest. 

 Originally the species had to aestivate during summer when clovers 



1 Trench, G. H. The Butterflies of the Eastern United States. New and rev. ed., Phila- 

 delphia, 1900, p. 130. 



2 Boll, J. Ueber Dimorphismus und Variation einiger Schmetterlinge Nord Amerikas. 

 Beut. Ent. Ztschr., Bd. 24, Heft 2, p. 241-248, 1880. 



