82 [ DISEASES OF CITRUS TREES 



established in these Islands since 1870-73. It is a 

 dark brown or rusty coloured scale, shaped like a 

 mussel or a comma, somewhat curved at one end, 

 surrounded by a narrow rim of wax, and measuring 4 or 

 5 m.m in length. The first shield under which is found 

 the head of the insect is of a darker colour. The three 

 shields representing the three moults are easily distin- 

 guishable in the female. The scale of the male insect is 

 smaller, and has only two shields; it is rarely crooked 

 and is generally deep purple brown in colour. The 

 purple scale has three broods in the year. Sometimes it 

 has a fourth brood, but as its larva does not develop so 

 fast as that of the Parlatoria, many larvae of the fourth 

 brood are washed down by rain. This scale insect 

 prefers the leaves shaded from the sun, and swarms in 

 the depressions on the undersurface of the leaves. Having 

 very powerful suctorial organs it sets thickly upon the 

 larger branches and sometimes on the stem, and ex- 

 hausts the tree to a greater extent than the Parlatoria. 

 When this parasite first made its appearance in Malta, 

 it caused a great deal of uneasiness, many groves suffer- 

 ing severely and becoming unproductive, and numbers 

 of young trees as well as trees in full bearing were killed 

 or became too much exhausted to.be retained. 



Mytilaspis fulva Targ-Tozz. is of the same form 

 as the preceding, but is slightly larger, and is of a lighter 

 colour, its margin on the concave side as a rule presenting 

 a marked undulation. Its variety, M. flavescens, is distin- 

 guishable chiefly on account of its very light or straw 

 colour. It is found along with the species, and both are 

 found mostly on the undersurface of the leaves and in 

 shaded situations, but are much less numerous than the 

 purple scale. 



The " long scale insect " of North America, 

 Mytilaspis Gloverii Ashmead, has a long narrow scale, 

 perfectly straight or only slightly curved. It has nearly 

 parallel sides. Its colour is brownish, and has the same 



