GALLS. 
167 
and then in the forests and hills may be expected to produce much that 
is new and second in interest to no other branch of insect bionomics. 
An excellent account of some of the features of this group is contain¬ 
ed in Sharp’s Insects. The student is referred to this, and it is needless 
to here reproduce a similar general account of a group of which almost 
nothing is known in India. 
G-ALLS. 
There are a number of insects, which live in the tissues of plants 
and whose activities produce an alteration of the structure of 
the plant, an unusual growth of tissue taking place, leading to the 
formation of a “gall.” Such galls are easily recognisable as quite 
distinct bodies, associated always with a particular insect and for each 
species of inhabitant assuming a peculiar form. 
Obviously this is a clearly distinct form of injury to the plant from 
that caused by an ordinary boring or leaf-eating insect, in which there is 
no growth of tissue except in so far as to heal the wound caused, and 
where the damage done is limited to the effect produced solely by the 
destruction of so much tissue. 
As a rule, the connected insect is in the gall, not necessarily in the 
fully developed gall but in it at some stage of its growth; put very broad¬ 
ly, the parent or the actual insect stimulates the tissues to an abnormal 
growth in which the gall insect lives ; the precise nature of this stimulus 
is not known for any of our galls but may be either poison or some agent 
introduced by the parent when laying eggs, or it may be a chemical or 
mechanical stimulus produced by the larval gall-insect inside the tissues. 
The growth of a gall does not always terminate with the emergence of 
the inhabiting insect and in some instances very large woody structures 
are produced on trees after the original gall-insect has emerged. 
Elsewhere, the Cynipidse are the especial gall-insects either inhabit¬ 
ing the gall by right or as inquilines (guests). The larvse of Nematus are 
said to form galls and insects of this family ( Tenthredinidce ), will possibly 
be found as gall inhabitants in India also. The Fig Insects of the family 
Chalcidce are probably gall producers, living in special gall flowers in the 
fig. An abnormal Buprestid (Ethon) is known to live in a gall 
and some of the Curculionidce also produce galls. Among Lepidoptera, 
a few Tineidce are known, and the transition from a boring larva to one 
that causes gall-formations is not a very wide one. Cecidomyiids are 
well known among the Diptera and are found in India behaving in 
this manner. Thrips (Thysanoptera) causes galls, as also do the three 
groups of Homoptera, the Psyllidce, Ap\idce and Coccidce; Psyllids are 
known to live in galls in India but do not appear to have been studied. 
Several have been reared from galls on leaves in India and it would 
