THE NUMBER OF MOULTS 617 



In Coleoptera the normal or usual number is not definitely known ; 

 Meloe moults five times, but this is a hypermetamorphic insect ; 

 Tribolium confusion has been carried by Mr. Chittenden through 

 seven moults. Phytonomus punctatus, the clover-leaf weevil, moults 

 three times, according to Riley, who has observed that Dermestes 

 vulpinus passes through seven larval stages. 



In the breeding jars, with plenty of food and a constant temperature of from 

 68 to 78 F., the larvae cast their 1st skin in from four to nine days, the great 

 majority, moulting at seven days. Under the same conditions the 2d skin was 

 cast at from four to seven days, the majority moulting at six days ; the 3d skin 

 at from three to six days, the majority moulting at five days ; and the 4th skin 

 at from three to six days, the majority moulting at five days ; the 5th skin at 

 from five to seven days, and the 6th skin at six days. There are thus seven 

 larval stages. (Report for 188-3, p. 260.) 



Riley has ascertained that by rearing isolated larvse of Tenebrio molitor, one 

 after being kept nearly a year had moulted 11 times, when it died. A second 

 larva, hatched June 5, had moulted 12 times by June 10 of the following year, 

 (1877), when it also died. Of T. obscurus three larvae were reared to the imago 

 state. One inoulted 11 times by Aug. 30 of the same year, pupated Jan. 20, 1877, 

 and finally became a beetle Feb. 7, 1877. The other two both moulted 12 times, 

 and reached the imago stage Feb. 18 and March 9, respectively. "All were, as 

 nearly as possible, under like conditions of food and surroundings, and in all 

 cases the moult that gave the pupa is not considered among the larval moults." 



Two larva? of the museum pest (Trogoderma tarsale) were kept by Riley in a 

 tight tin box with an old silkworm cocoon. "They were half-grown when 

 placed in the box. On Nov. 8, 1880, there were in the box 28 larva skins, all 

 very much of a size, the larva having apparently grown but little. The skins 

 were removed and the box closed again as tightly as possible. Recently, or after 

 a lapse of two years, the box was again opened and we found one of the larvae 

 dead and shrivelled up ; but the other was living and apparently not changed in 

 appearance. There were 15 larva skins in the box. He could not tell when 

 the one larva died, but it is certain that within a little more than three and a 

 half years, two larvas shed not less than 43 skins, and that one larva did not, 

 during that time, appreciably increase in size. " We know of no observations 

 which indicate the normal or average length of life, or number of moults in 

 either Tenebrio or Trogoderma, but it is safe to assume from what is known, 

 in these respects, of allied species, that in both the instances here referred to, but 

 particularly in the case of Trogoderma, development was retarded by insufficient 

 nutrition, and that the frequent moulting and slow growth resulted therefrom, 

 and were correlated." * Further observations such as these are greatly needed. 



Of the Siphonaptera the common cat and dog flea (Pulex ser- 

 raticeps) moults three times before pupating. (Howard.) 



In Lepidoptera the usual or average number of moults is four, 

 but the number varies considerably, the greatest number yet known 

 occurring in Phyrrarctia Isabella, which, Dr. Dyar informs me, moults 

 10 times. 



From Dyar's observations it appears that there are usually five 



1 American Naturalist, xvii, May, 1883, pp. 547, 548. 



