APHIDID.*:. 277 



ScHizoNEL'KA ULMi (Linn.) 



The arboreal species most injurious in this country and throughout 

 Europe is the Srhizoneiira uhni (Linn.), and the most injurious 

 arV)oreal species in America is known as ScMzoneura amerirana 

 (Uiley).i 



The description given by European writers was suggestive of the two 

 species being identical ; but Professor Riley, on closer examination, 

 found that the two species differ from each other in their methods of 

 damage and structural details, thus showing that while we may deplore 

 specific hair-splitting, hasty grouping is far from commendable. 



Riley maintained that, considered as a pseudo-gall, the chief differ- 

 ence in the two species is that the stem-mother of 8. ulmi attacks tlie 

 upper side of the leaf, and the injured leaf in consequence rolls over ; 

 whereas the stem-mother of S. americana attacks the under side of the 

 leaf, and the injured portion rolls under. This observation was based 

 by Prof. Riley on a specimen sent from England by Mr Buckton, but 

 it certainly does not coincide with our own species, S. uhvi, inasmuch 

 as the queen-mother attacks the under side of the leaf and rolls under 

 (fig. 260). 



Hence it is evident that we must have recourse to foreign literature, 

 for though the various species may be more or less local, the genus 

 may often be cosmopolitan. A more comprehensive view of the 

 genus will give a better grasp of the species. 



The queen-mother may be found about the middle of May. She is 

 apterous, of a dark-olive colour, mottled with dark-bluish tints, like the 

 gloss on black grapes. The creature is considerably larger than any 

 of her offspring, which may be found either along with her or after 

 her death. The body is slightly covered with a cottony exudation 

 arising from a series of pores on the back. In comparison with the 

 body, the head and thorax are very small. The antennas and legs are 

 short, hence the creature is very helpless. The antennae are composed 

 of six joints, the third being nearly half the entire length. It is 

 highly probable that those stem-mothers hatch from eggs laid the 

 previous autumn. 



The winged specimens may be found very plentifully by the middle 

 of June in the rolled elm leaves. The body of the female is wholly 

 black in colour: the eyes are also black. The third joint of the 

 ^ Insects Injurious to Forest Trees. Packard, U.S.A. 1890. 



