DISEASES OF CITRUS TREES ] 77 



in the centre if round or at one end if oval there is a 

 darker spot of reddish brown, which is the first scale, 

 and has a mesial ridge which divides it into two parts. 

 The scale of the male is much smaller and elongated ; 

 it is white having a reddish brown shield at one extremity 

 as in the female. This scale is now common on the 

 trunk and branches of Citrus trees growing in the 

 shade. 



Diaspis Colvei Penzig, is probably only a variety 

 of the preceding and is found along with it. 



Aonidia Gennadii Targ., appears to be a native of 

 Australia and New Zealand, whence according to Corn- 

 stock, it has been imported into California. It bears 

 the name of Mr. Gennadius who found it in 1880 upon 

 the leaves of the lemon tree cultivated in Greece. It 

 has a round scale of a dirty greenish colour, having 

 a central prominence of the same colour and pellucid 

 margin. The scale of the male is elongated and irregu- 

 larly oval, with the pointed oval first shield situated 

 at one end, instead of being central as in the female. 

 This insect has not been seen in our orange groves. In 

 California it is a common parasite upon the orange and 

 lemon. In Greece it seems to prefer the lemon. 



Aspidiotus Hederae Val., or A. Ceratoniae Signoret, 

 is another species similar to the preceding. Its colour 

 is greyish, having the central protuberance or exuviae 

 of a dull orange colour. It is very common on the 

 Carob and on ornamental trees and shrubs, particularly 

 on the Oleander or Rose-bay tree, on Ivy and on 

 Acacias, but is rarely met with on Citrus trees. 



Aspidiotus Limonii Signoret, is not very prevalent 

 in our Citrus groves. It is usually seen upon young 

 lemon trees situated in shady and sheltered situations. It 

 is a small round white scale as large as a pin's head, 

 having a flattened conical protuberance of a yellowish 

 colour in the centre, due to the body of the insect 



