48 U.S. NATIONAL MUSEUM BULLETIN 256 



and the hindwings are pearly white except for the narrow dark 

 marginal line. The proportion of males and females varies within cer- 

 tain limits; normally there is a preponderance of males, the average 

 number of females being 46 to 48 percent. The average longevity of 

 the adult is 9 days, the maximum record being 18 days. 



The number of eggs in a stick varies greatly, but the average example 

 contains from 76 to 90 eggs. The maximum record is a stick contain- 

 ing 150 eggs. Each female may deposit several eggsticks; 3 or 4 tend 

 to be the normal procedure, but frequently from 8 to 12 are laid. 

 Where a moth produces several sticks, the first two or three contain 

 the greatest number of eggs and the last two or three the smallest 

 number of eggs. 



The fecundity of the females is most variable. The greatest number 

 of eggs deposited by one individual has been 392. In isolation experi- 

 ments many females have laid between 200 and 300 eggs, but com- 

 paratively few have deposited more than the latter number. 



High averages from many moths are cited as follows: 



With large numbers of moths in oviposition cages, the usual return 

 has been 90 to 110 eggs per female. 



The incubation period depends on temperature, the shortest time 

 recorded being 18 days. The eggs usually hatch in 23 to 28 days 

 during January and February, in 30 to 32 days during February and 

 March, in 40 to 45 days during March and April, in 40 to 50 days 

 during September and October, and in 28 to 32 days during October 

 and November. For out-of-season eggs deposited in autumn and 

 hatched during winter, an extreme incubation period of 132 days has 

 been reported. 



On hatching, all larvae from one eggstick enter the plant at one 

 point. At first they feed just beneath the cuticle, but soon penetrate 

 deeper. They tunnel freely wittiin the cladodes, consuming the whole 

 of the interior except the vascular bundles and leaving the undamaged 

 cuticle as a transparent tissue. However, their burrowing usually 

 causes bacterial activity which hastens the destruction of the segments. 

 When one cladode has been eaten out or has decayed, the larvae 

 may penetrate into the next segment. More frequently they vacate 

 the damaged segment, crawl over the surface of die plant, and enter 

 a fresh cladode; this action generally results in the division of the 



