64 
BRITISH APHIDES. 
unlimited, yet in great measure it is controlled and 
determined by insufficient food and reduced tempe- 
rature. Further he says, that certain species, feeding 
on herbaceous plants which fruit early in the year and 
then wither, produce males and apterous oviparous 
females in ilie middle of the summer. Also, that the 
same thing occurs when the food-plants rapidly become 
woody in texture. On the contrary, where Aphides get 
their nourishment from plants persistent throughout 
the year, the males and the matured females, as a rule, 
do not appear until late autumn or early winter. It is 
true that Kyber’s remarks here particularly refer to the 
causes which he considers defer the complete develop- 
ment of the cycle by the appearance of those indi- 
viduals which close that cycle, but it cannot be doubted 
that the same influences do also affect, within cer- 
tain limits, the external forms, sizes, and colours of 
Aphides. 
Kaltenbach’s grouping of the old genus Aphis under 
indices has been more completely developed by Koch, 
who threw together a number of allied forms and con- 
structed several genera which have met with general 
acceptance by modern Entomologists. 
Probably the undue multiplication of species and the 
confusion in the synonymy of Aphis led Prof. 
Passerini,^ of Parma, in 1860, to undertake an entire 
revision of the subject. He has done good service by 
tabulating the most marked characteristics of the 
various genera, and in such a manner that a good 
clue is afforded the student by which he may satis- 
factorily track any insect under examination to its 
correct place in his system. His tables are compre- 
hensive, and such being the case the diagnosis of each 
species is included within very moderate limits of type. 
Subsequently to his work on the Italian Aphides he 
published an alphabetical list of the chief plants he 
found to be most infested by them, due attention being 
* G. Passerini, ‘ Gli Afidi con un Prospetto dei Generi ed alcune 
Specie Nnove Italiani,’ Parma. 
