APHIDiE. 
745 
of our species are temperate forms which are active only in the cold 
weather and have to live over, not cold but hot weather ; others are 
active throughout the year when food is available. The commonest 
aphides appear to have no sexual generation in the plains and, though 
much is obscure, it is at present reasonable to believe that the altered 
climatic conditions produce different sexual habits. Aphides are uni¬ 
versally plant feeders, living on the sap of plants. Several common 
cultivated plants are very seriously attacked and it is doubtful if any 
cultivated plant will not be found to be the host of some species. 
A sweet liquid is produced by these insects and is either excreted at 
the anus or secreted from the siphons. This liquid (honeydew), which 
is produced by many homopterous in¬ 
sects, is a favourite food of ants. Cer¬ 
tain species of ants derive a large part 
of their food from aphides and it is not 
uncommon to see the aphides cared 
for by the ants, shelters built for them 
and their enemies kept off. Many 
have more intimate relations with 
ants but our common species are free- 
living and are only visited by ants. 
Many other insects feed on the honey- 
dew when it falls in abundance on the 
leaves, but only ants are known to 
obtain it direct from the siphons of 
the aphides. The enemies of aphides are proportionate to their 
enormous power of increase and are the sole check upon them. 
Aphides are parasitised by Braconids, are devoured by the larvae and 
imagines of Coccinellid beetles, by the maggots of Syrphus and other 
flies, by the grubs of the Hemerobiids. Fungoid diseases destroy 
them under favourable conditions and birds have been seen to eat 
them. Were it not for these checks the aphides would, under their 
ordinary rate of increase, render the earth uninhabitable within a short 
time. 
The classification of Aphidce is a disgrace to modern entomology, 
and the group has not been properly studied in recent years. Buck- 
ton’s British Aphides deals with the group as a whole, but the genera are 
Fig. 518- Rhizobius jujtjbjs. 
(I. M. N.) 
