June, '17] QUAYLE: COCCUS CITRICOLA AND C. HESPERIDUM 375 



color of gray or dirty white. Hesperidimi has the color pigment 

 coalesced in more or less definite areas and the ground color is dis- 

 tinctly yellowish. In lustre, citricola is dull while hesperidum is shiny. 



Hesperidum varies in shape more than citricola. The former may be 

 straight on one side and curved on the other, or otherwise different 

 from the usual oval, particularly, if they are situated along the midrib 

 or if the specimens are crowded closely together. 



It is in their life history and habits that the two species are markedly 

 different. In citricola there is but one generation a year, while in 

 hesperidum there are three or four over-lapping generations. Indi- 

 viduals of different sizes that may be seen at any one time in the case 

 of hesperidum furnish a ready means of distinguishing the two species. 

 From August to March all living specimens of citricola are uniformly 

 of small size. During ]\Iay, June and July there may be two sizes 

 of this species, either mature individuals or very small specimens. 

 Citricola is oviparous while hesperidum is ovoviviparous. The male of 

 citricola is only occasionally seen. On citrus trees the puparium of the 

 male of the black scale (Saissetia oleoe) is likely to be mistaken for 

 that of citricola. The puparium of citricola may be distinguished 

 from that of the black scale by the broader band, consisting of numer- 

 ous cross lines, bordering the coronet. There are several references 

 that refer to the male of hesperidum, but in the writer's judgment 

 the proof in these references is not sufficient to say positively that the 

 male described was of this species. Male puparia have been taken 

 in the midst of infestations of hesperidum, but in all cases observed, 

 they proved to be that of S. oleoe, L. corni or C. citricola, infestations 

 of which were in the immediate vicinity. It is not unlikely that the 

 male of hesperidum occurs, but evidence of the fact in the references 

 at hand seems insufficient. 



The host plants of hesperidum include a ver}' wide range in number 

 and variety. Those of citricola, as far as observed, include all varieties 

 of citrus, hackberrj^, Celtis occidentalis; buckthorn, Rhamnus crocea; 

 pomegranate, Punica granatum; night shade. Solarium douglassi; 

 English walnut, Juglans regia; and Elm, Ulmus americana. The host 

 plants named, other than citrus, were found infested in more or less 

 close proximity to citrus. The discover j" of the scale on hackberry, 

 some of which trees were said to have been imported from Japan, 

 led to the suspicion that the scale may have come from that country. 

 But in correspondence with entomologists in Japan it is learned that 

 C. citricola is not known to occur there, or at least is not native to the 

 country. Mr. C. P. Clausen writes that he has seen what he considers 

 to be C. citricola on citrus in Japan, and that it probably has been 

 introduced from California. 



