76 [ DISEASES OF CITRUS TREES 



The SCALE INSECTS, a class of true parasites, have 

 acquired an evil celebrity all over the world. Trees, 

 shrubs and plants are equally subject to their parasitism. 

 The same scale insect may be found on several species 

 of vegetables, and the same tree may be liable to the 

 attacks of several species of scale insects. They are a 

 numerous and prosperous class of very easy propagation. 

 The damage caused by a single scale insect may be 

 overlooked, but they derive their dangerous qualities from 

 their vast numbers. When first imported into a new 

 region they are slow to establish themselves, and if 

 remedial measures are immediately taken we may hope 

 to suppress them, as has been the case lately with 

 Diaspis pentagona imported from Sicily along with some 

 ornamental shrubs. But if they happen to obtain a 

 footing and to become established, nothing can prevent 

 them from extending in every direction. Were it not 

 for -their numerous enemies, the cultivation of Citrus trees, 

 as well as of many other fruit and ornamental trees, 

 on a commercial or extensive basis, would be imprac- 

 ticable, and no country ever succeeded, either by natural 

 or by artificial means, to stamp out entirely any kind 

 of scale insect after it had been fully established. There 

 are no less than 24 species of scale insects affecting 

 Citrus trees. Twelve of them are present in Malta, 

 with great probability of fresh additions, but with no 

 hope of seeing this number diminish. 



Chionaspis Citri Comstock, has a minute somewhat 

 fan-like scale of a blackish brown colour, with a gray 

 margin ; the first shield is brownish yellow. This para- 

 site exists in Louisiana and neighbouring states. It has 

 not been noted in Malta, although we have other species 

 of Chionaspis on the Pine and other Conifers. 



Diaspis Monserrati Colvee, is another scale whose 

 presence was first noticed in the Botanical Gardens at 

 Valenza in Spain. The scale of the female is slightly 

 oval, sometimes perfectly round, of a grey colour. But 



