300 AKNUAL REPORT. 



That this is the case is of easy observaftion, especially la regard to many of our 

 garden species, and I need but call your attention to the cabbage or squash aphis, 

 as all who have observed these species probably know that in spring they are found 

 in comparatively few but in very large colonies, and that while one plant may be 

 badly infested, the one next to it may all together be free from the pest, as this 

 flrst brood seldom does wander from one plant to another. But if We examine the 

 field after the second brood has come to its greatest development, we can usually 

 find not only every plant has almost every leaf with a number of young colonies 

 on them. These young colonies can easily be recognized in that they consist of a 

 winged female )vith a smaller or greater number of wingless individuals close 

 around her of all sizes and ages. The species inhabiting the squash is especially 

 conspicuous in this respect, as the females usually choose the outer border of the 

 leaf where to establish their colony, and therefore a series of colonies can often be 

 seen encircling the leaf on the under side. 



In nature the preservation of a species is always most admirably provided for. 



So the plant- lice, that in the wingless form would be incapable to disperse the 

 species successfully, as even a small stream of water would make an cfEectual 

 barrier, we find that it is most perfectly performed in that some of the viviparous 

 females, in height of the summer, as the most favorable time for flight, acquire 

 wings in order to do this duty. 



FALL BROOD. 



In the fall quite a different brood makes its appearance, consisting of sexually 

 developed males and females. As before stated, it has usually been considered 

 that all the individuals of this last brood, or fall brood, were winged, it is now 

 known that not only the females, as a rule, are wingless, but that the males are 

 also sometimes wingless. I have observed the oviparous females as wingless in the 

 following genera: Siphonophora, Myzus, Rhopalosiphum, Aphis, Chaitophorus, 

 Lachnus, Caliipterus, Mattopoda, Schizaueura and Pemphigus. The only case in 

 Tvhich it is positively known that the ovipraous females are winged is some of the 

 smaller and lower genera. The largest genus aphis is still clothed in much mj'stery, 

 the life history of but comparatively few species being well known. Yet all that 

 is at present known goes to show that the oviparous females are wingless. 



The occurrence of wingless males has been noticed in several cases, though it is 

 still considered as an open question by some entomologists. We usually do find 

 the males as winged, and the occurrence of wingless can only be considered as an 

 exception, but an exception that is not as rare as generally supposed. In the 

 genus Siphonophora I have observed this form as occurring in several species; 

 usually only as a few individuals, the majority being winged. In one species, 

 belonging to this same genus, all males observed were wingless, not a single winged 

 specimen could be found. This species is found on the wormwood or "sage" 

 {Artemisia frigida, Wild.) growing plentifully along the bluffs of the Mississippi 

 in this vicinity, and as it is apparently new to science I have described it as such 

 in the 14tli annual report of the Geological and Natural History Survey of Min- 

 nesota, naming it Siphonophora frigida, as found on this northern variety of worm- 

 wood. As I have been able to follow nearly the whole life-history of this species 

 I shall give it as being peculiar in respect to the wingless males, and at the same 



