LECANIUM. 



Technical Bulletin No. 48 



By R. H. Pettit and Eugenia McDanicl. 



The genus Lecanium includes forms of Coccids having each an anal 

 cleft at the base of which is placed a pair of small triangular plates 

 known as the anal-plates. The form may be flat or almost spherical, 

 the color is usually brown but may be quite brilliant and conspicuous 

 in some forms. The young may be produced alive or eggs may be laid 

 which remain under the body of the mother until hatching time. The 

 skin may be shiny or dull, naked or clothed with a thin sheet of waxy 

 material or with a waxy secretion resembling cotton or meal, but in 

 no case is the wax in the form of plates as in Ceroplastes, or are the 

 eggs laid in a nidus of cottony material pushed out behind the insect 

 as in the case of Pulvinaria. 



The only characters apparently thus far discovered for separating 

 the members of Lecanium into species, lack stability. This naturally 

 accounts for the multitude of species recorded; too many of the work- 

 ers contenting themselves with insufficient exploration or else becoming 

 discouraged and publishing their impressions at the time of dropping 

 the group. 



The members of what we consider L. corni find themselves distributed 

 over a multitude of host-plants and seem to thrive nnder various 

 climatic conditions. They vary in size, shape, color and somewhat in 

 derm markings, characters of the anal-plates, and in the antennal char- 

 acters. The appearance of the derm seems to be influenced strongly by 

 tlie age of the subject, by the method of its preparation, and by the time 

 of boiling. Also there is a variation among individuals which is of 

 course, to be expected. Just what are the limits of variation between 

 species, and just where we shall cease to regard, individuals as merely 

 differing one from another, and to consider them as different races; 

 just where races merge into varieties, and varieties into species, must, 

 as yet, be a matter of individual opinion, and must remain so until 

 some one finds characters of a more stable nature on which to divide 

 the members of this puzzling and baffling genus. 



It would seem that the peculiar tessellations so conspicuous in the 

 derms of some examples are of less value than was anticipated, since 

 their appearance depends, more or less, on the age and vigor of the 

 individual specimen and on the preparation of the mount. 



In order to examine the anal-plates and the derms of Lecania, it is 

 necessary to clear the specimen and often desirable to make permanent 

 mounts. We have found the following method fairly satisfactory for 

 this purpose: 



First, specimens, either fresh or dry, are boiled in 10% sodium 

 hydrate (caustic soda) until they begin to show a slight bleaching. 

 They are then boiled in one or two changes of distilled water, until 



