356 



PSYCHE. 



[March 1896. 



lent colonies, so closely resembling the 

 bark that they are difficult to detect. 

 The males of this species are wingless. 

 The oviparous females seem to take 

 more care than do the spotted ones in 

 depositing their eggs in the crevices of 

 rough bark where the peculiar whitish 

 covering of each helps greatly to con- 

 ceal it. 



There are two other aphides of the 

 genus Melanoxanthus which live upon 

 willow twigs but difler from those men- 

 tioned above in habits of oviposition.' 

 The Bicolored Melanoxanthus {M. hl- 

 color) is a rather rare species found in 

 many of the western States. The males 

 are winged, and the yellowish brown 

 oviparous females deposit their eggs in 

 the crevices aliout the buds : tlie latter 

 after a short exposure to the air become 

 shining black with none of the floccu- 

 lent covering found on the eggs of the 

 other species. The most abundant 

 member of the genus is that sometimes 

 called the Willow Grove Aphis {M. 

 salicti) which is similar to the spotted 

 form, but without the conspicuous 

 white spots. It lives in large colonies 

 on tiie twigs and branches. The winged 

 males and oviparous females develop 

 in autumn, and the latter oviposit on 

 the twigs about the buds. 



One of the laigest aphides living 

 upon twigs is the Sycamore Lachnus 

 (/.. platanicola) which occasionally 

 becomes extremely abundant in man}' 

 sections of the United States. The 

 sexed forms appear early in autumn, 

 and eggs are deposited in enormous 

 numbers upon the bark. 



Some of the aphides affecting herba- 



ceous plants complete their yearly cycle 

 upon them. The large reddish brown 

 species {^Nectarophora rudbeckiae) so 

 commonly foun<l upon composite plants 

 of the genus Solidago and Lactuca is 

 one of these. In studying its autumn 

 history in Illinois a few years ago, I 

 found that the sexed forms developed 

 during October, the males havine 

 wings. Eggs were occasionally depos- 

 ited upon the old stems of wild lettuce 

 {Lactuca caf7adcn>e) , but much more 

 commonly upon the under leaf surface 

 of the young, first-year plants of Lac- 

 tuca and the closely allied Muhlen- 

 bergia. Evidently the ciiances of sur- 

 vival and future development are bettei- 

 in the case of the eggs deposited upon 

 the leaves of j-oung biennials or peren- 

 nials, than of those fastened to the old 

 stems which are liable to be broken off 

 and blown or washed away, so that if 

 the eggs survived the young aphides 

 would not be likely to find suitable food 

 at hand. In such cases a system of 

 natural elimination must tend toward 

 the preservation of the forms oviposit- 

 ing upon the young plants. 



Perhaps the most remarkable fact 

 connected with the hibernation of 

 aphides is that of the preservation of 

 the eggs through the winter in the 

 nests of ants. This was discovered 

 long ago by Huber. and has since been 

 abundantly confirmed by .Schmarda, 

 Luljbock and others. Ruber's account 

 is so interesting, and apparently so 

 little known, that I quote it at some 

 length* : — 



* The Natural History of Ants by M. P. Huber. Trans- 

 lated by J- R. Johnson. London, 1S20, pp. 240-245. 



