APHIDID.E. 



321 



As compared with the preceding genus, the rostrum is comparatively 

 short, the antennas short and six-jointed. The wings are similar to 

 those of Pemphigus, "except that there is only one oblique vein in 

 the lower wing." 



The gall attains its full size prior to the complete development of 

 the insect. The antennas are four-jointed, the rostrum rather long in 

 comparison with the body, and legs slightly hairy. Colour dark oak, 

 and the insects very sluggish. It is 

 very harmful to isolated elms, killing 

 the leaves * in many parts of the 

 country. 



Tribe CHERMESIN.E. 



Perhaps in the whole realm of 

 forest entomology there is no tribe 

 of insects which presents such pecu- 

 liar difficulties as the Chermesinae, 

 inasmuch as it is most difficult to 

 present the biological importance, as 

 revealed by the present state of Fi s- 297 -- 

 our scientific knowledge, and the 

 exact discrimination of our so-called species in such an amalgamated 

 form as will be correct to the scientist, and also intelligible to the 

 practical man. In other words, we have, in this group, two problems 

 to face viz., the alternation of a species from host-plant to host- 

 plant, and on the other hand the determination of the so-called species 

 on their respective host-plants as associated with their own peculiar 

 injuries. 



First, let us consider the alternating generations as given by Judeich 

 and ^"itsche, 1 and more recently by Niisslin 2 from Cholodkovsky. In 

 the former, two classes are given viz., (1) Continuation or remaining 

 on spruce, with clear parthenogenetic reproduction ; (2) partly emi- 

 grating from the spruce to the larch, with parthenogenetic or sexual 

 reproduction. In the latter, which has been carefully worked out by 

 Cholodkovskjr, the gist of it may be summed up as follows : 



Typically the Chermes show five generations and an exchange of 

 host-plant. The principal host-plant is always the spruce ; but only 



1 Forstinsektenkunde. 



2 Leitfaden der Forstinsektenkunde. 



-Galls o/Tetraneura ulmi on 

 leaves of elm. 



