18 INSECTS AFFECTING TH& ORANGE. 



means of which it is enabled to reach and fertilize the females under 

 their scales. 



Prof. J. H. Comstock, whose minute and exhaustive study of the life- 

 histories of certain of our common Scale-insects has left little to be added 

 by subsequent observers, has pointed out that the lives of these insects 

 are divided by their metamorphoses into nearly equal intervals. In 

 the words of this author, " the three intervals between the birth of the 

 female and the first molt, between the latter and the second molt, and 

 between this and the beginning of ovipositiou are about equal."* The 

 first molt in the male, and also its second molt, or entrance into pupa, 

 take place at nearly the same time with the molts of the female. The 

 existence of the male, however, terminates before the completion of the 

 third interval by the female. 



The interval in which the eggs are laid and hatched, and the young 

 larvae desert the parent scale, is about equal to the preceding inter- 

 vals. This fourth period completes the cycle of development, and its 

 close witnesses the death of the female, following the departure of her 

 progeny. 



During the spring and early summer, in the laboratory at Washing- 

 ton, twenty days appears to have been the mean duration of each in- 

 terval $ ill the open air in Florida there is considerable acceleration, due 

 to the warmer climate. This is apparent especially in the later stages 

 of development, which are greatly shortened in summer. The first 

 molt usually takes place within twenty days after hatching, but this 

 first period, although more constant than the following, varies with the 

 eeason or in different species, from sixteen to twenty -four days. The 

 whole cycle, or brood period in winter, may cover three months, but in 

 summer, it is reduced to five or six weeks. 



Nature of the scale covering. As was first clearly pointed out by 

 Prof. C. V. Riley (see Fifth Missouri Entomological Eeport, p. 80) the 

 scale of the Diaspina3 is a shield-like structure, covering the in- 

 sect above, and wholly or partially protecting it beneath. It is con 

 structed, as we have seen, in part of tbe molted skins of the insect, but 

 mainly of a horny excretion, covering or surrounding the latter, and de- 

 posited by the Ooccid in numerous fine, overlapping layers. The under 

 layer is thinner, and, although perhaps a separate piece, is firmly united 

 to the upper scale at the edges, so that the latter appear to be turned 

 under at the sides. In the long scales the ventral plate consists of a 

 flange along each side, leaving in the middle an open crevice; but in 

 the oval or circular scales it forms an unbroken shield, which entirely 

 separates the body of the insect from contact with the bark. 



The scale js permanently fastened upon the tree, and so closely molded 

 to its surface that the pores of the bark or the stomataof the leaf are 

 seen plainly stamped upon it when removed. 



The materials of which the scale is constructed are very indestructi- 



* Report of Commissioner of Agriculture for 1880, p. 280. 





