282 FOREST ENTOMOLOGY. 



As compared with the preceding genus, the rostrum is comparatively 

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

 those oi Pemphujus, "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 antenna are four-jointed, the rostrum rather long in 

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

 and the insects very sluggish. In 

 several places in the south of Eng- 

 land it is very injurious to the foli- 

 age of isolated elms. 



Tribe CHERMESIN.^.i 



Perhaps in the whole realm of 

 forest entomology there is no tribe 

 of insects which presents such pecu- 

 liar difficulties as the Chermesinse, 

 inasmuch as it is most difficult to 

 present the biological importance, as 

 Fig. 26s.-Gf;».s'o/Tetraneura mini o/( revealed by the present state of 



haves of dm. "^ ^ 



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 Xitsche,- and more recently by Niisslin^ from Cholodkovsky. In 

 the former, tAvo 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 

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



Typically the Chermes on spruce show five generations and an 



^ A detailed study of the tribe Chermesinse, together with its associations 

 as regards difficult problems iu forestry, is at present being done by Mr E. R. 

 Burdon, Cambridge University. 



2 Forstinsektenkunde. ^ Leitfaden der Forstiusektenkunde. 



