254 Transactions. — Zoology. 



different families of the class Insecta, the Hymenoptera and 

 the Dijjtera, seem to have made common cause against the 

 plant, and live in close alliance at its expense. A good deal 

 of the straggling natm-e and ungraceful appearance of the 

 shrub is due to their attacks, and doubtless if one could insure 

 freedom from them the Olearta might be made much more 

 ornamental than it is. Of these two insects, one, the 

 hymenopter, preys apparently only on the buds and young 

 shoots ; the other infests both buds and leaves. 



The "galls" produced on the plant are of two kinds. 

 The one affecting the young shoots and buds has the ap- 

 pearance of large excrescences formed round the axils of the 

 twigs, as if in those spots an abnormally large number of 

 shoots had begun to grow out, and, having their growth 

 suddenly arrested, had coalesced in an irregular mass, their 

 stunted leaves crushed up and crowded together. Examples 

 of these are shown in Plate XL, fig. 1, and Plate XII., fig. 1. It 

 will be observed that there is a slight difference between these 

 two, the leaflets in one being much smaller and more crowded 

 than in the other. My experience has been that in the larger 

 one (Plate XII.) only the dipterous insect lives ; in the smaller 

 one (Plate XL) mostly the hymenopteroiis, but frequently, 

 together wdth it, the dipteron also. A section of either of 

 these galls will show (as in Plate XL, fig. 2) a colony of insects, 

 in the pupa or in the larva stages, living in cells within it. 

 The differences between the two insects may be easily seen 

 by the larger size of the dipteron and therefore of its cell, 

 independently of the differences of colour given below. 



The other kind of gall is exclusively the work of the 

 dipteron, and takes the form of blisters on the leaves, as 

 shown in Plate XII., fig. 1, and in section, fig. la. When the 

 perfect insect is ready to emerge it breaks a hole through the 

 leaf, and the pupa thrusts itself out for about half its length 

 before the fly emerges, as shown in the figure. 



Of these two galls the last, on the leaves, would not 

 probably be hurtful ; the other, which arrests and deforms the 

 growth of the young shoots, must exercise a baneful effect 

 upon the vigour of the plant. 



The two insects appear to go through their transformations 

 and perform their work at the same periods of the year. The 

 eggs are laid about October, and the larvae emerge from them 

 in a week or ten days. The larvae seem to change to pupse at 

 different intervals — sometimes in early summer, sometimes not 

 until the following spring. The perfect flies emerge about 

 October, and probably, on any particular shrub, all about the 

 same time. Procreation takes place immediately. I have 

 seen a male and a female emerge from a gall almost at the 

 same moment, and five minutes afterwards copulate. 



