DISCUSSION OF GENERA AND SPECIES 37 



Lecanium cerasorum Ckll. 



1915. Lecanium cerasorum Ckll.; Essig, "Injurious and Beneficial Insects of 

 California," ed. 2, p. 145, fig. 124. 



This is an introducd species that is now established in the vicinity 

 of San Jose, where it occurs on fruit trees. 



Structurally this appears to be inseparable from L. excrescens n. sp., 

 which is described below, but the two differ greatly in appearance. As 

 maturity approaches L. excrescens becomes covered with a thick coating 

 of loose, white secretion, while L. cerasorum remains naked throughout. 

 It is a very conspicuous object, the dorsum being marked with a series of 

 regularly arranged white spots (well shown in the figure given by Essig), 

 from which it has derived the popular name "calico scale." 



There is nothing in the original description of this species that 

 will permit its identification, and there is a possibility that the species here 

 recorded as cerasorum is incorrectly determined. 



Lecanium pruinosum (Coq.). 

 What is supposed to be this species is rather common on walnut. 



Lecanium pubescens Ehrh. 



Under this name there has been described from this region a form 

 which occurs quite commonly on Quercus agrifolia and on Aesculus cali- 

 fornicus. It differs from typical L. corni only in its somewhat larger size, 

 the presence of rather evident, transverse dark bands in life and a slight 

 amount of loose secretion (the "very soft hair" of the original descrip- 

 tion). Structurally it does not differ from L. corni. 



Lecanium excrescens n. sp. 



Fig. 16. 



Type host and locality. From cultivated English walnut, Palo Alto, 

 Calif. It occurs in this vicinity on almond and maple also. 



Habit. A very large species, attaining a height of 8-10 mm. and a 

 diameter of 10 mm. in the largest examples. In form the fully developed 

 scales are very high convex (Fig. 16A), with the margin nearly perpen- 

 dicular to the base, which is nearly circular in outline. During the last 

 instar the scale becomes entirely covered with a thick coating of rather 

 fluffy, white secretionary matter which disappears in weathered individ- 

 uals, the latter being very dark brown and slightly shiny. 



In the second and early third stages the dorsum is entirely destitute 

 of secretion except for a number of symmetrically and characteristically 



