140 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—I9Q22 
habitat, as Siphonophora frigidae. Williams described several addi- 
tional species from Artemisias and still later Gillette and Wilson have 
increased our knowledge of these forms. There 1s something distine- 
tive about all our Artemisia forms, tho most of them can be associated 
with the Aphidini and Macrosiphini. There are some that can not so 
be placed and probably represent a different stock, as indicated by 
the present tribe. One would not expect the sage-bush areas of the 
great western plains to be rich for collecting aphids, but a score of 
species are now known and many remain to be made known. Miunne- 
sota is on the border of this area and can be considered to come 
within it, as several different Artemisias are found over the state, which 
become infested with these western forms from time to time. 
It has long been a puzzle to me to account for this peculiar sage- 
bush fauna, as most of them can easily be associated with various 
tribes, the Aphidini, Chaitophorini, Myzini, and Macrosiphini. They 
may be looked upon as a biological group and not a phylogenetic, with 
the exception of the Microsiphini. The geology of the great plains 
may give us the clue as to the origin of the fauna. In the early stage 
of the North American continent the western plains did not exist, as 
geologists tell us, but the land was only slightly above the sea level 
and the flora and fauna were probably the same for both the east-and 
the west. With the gradual elevation of the west, the original flora and 
fauna would tend to disappear, except for those forms that were able to 
adapt themselves to the new and changed condition, and a new flora, 
adapted to the changing conditions, would come in, replacing the old 
and disappearing one. The Artemisias were some of those new im- 
migrants, and have now become the dominant forms. The various 
forms of Aphis, Chaitophorus, Myzus, and Macrosiphum persisted 
only to the extent that they became adapted to the dominant Artemi- 
sias; while Lachnus, Callipterus, and Pemphigus have disappeared 
from those areas. One genus of the Microsiphini is well represented 
in Minnesota : 
acl Génus (MIC RO STP HUM 8 ra. ere ccs aie ne ee ee ne ee a OI 
gt. Genus MICROSIPHUM Cholodkovsky, 1908. Type: Micro- 
siphum ptarmicae Cholodkovsky, 1908. Has the general appearance 
of a small Macrosiphum with very short cornicles. 
(98) MICROSIPHUM ARTEMISIAE (Gillette) Wilson, 1915 
Color wine red; found on Artemisia Iudoviciana. 
g2. Tribe MACROSIPHINI. Size large and gradually pointed 
posteriorly ; antennae usually much longer than the body; sensilla of 
