<jorded, the average length of larval stage was 267 days; tlie luaxi- 

 miira, 356 days; the mininiuin, 179 days. Or, reduced to months, 

 the average length of larval stage was about nine months; the maxi- 

 niiini, twelve months; and the minimum, six months. It is at once 

 apparent that the astonishing variation in the length of life-cycle 

 of this species is due to the variation in length of the larval, or grub, 

 stage, the egg and pupal stages showing very little variation in dura- 

 tion. (See charts on Plate VIII.) 



Nine out of ten months (or 90 per cent) of the insect's normal 

 life below ground are spent in the larval, or grub, stage. During 

 most of this time the grub is doing actual damage to cane by feeding 

 upon the roots. 



The length of larval period, secured by adding together the aver- 

 ages of the three instars, amounts to 266 days. This constitutes a 

 very good check on the al)ove average of 267 daj^s, computed from 

 the whole larval stage of 50 larvae, since a good many of the grubs 

 iiom which tlie instar averages were taken never reached pupation, 

 and conversely, a majority of the grubs whose exact dates of egg 

 hatching and of pupation were recorded, were not observed and re- 

 corded as to their molts; so that the two results were taken to a large 

 extent from ditferent series of gruljs. 



The explanation for fifty grul)s having reached the pupal stage. 

 Avhereas only about twenty reached the adult, lies in the fact that 

 at the time of pupation the grub is particularly susceptible to injury 

 by handling, or by attack of the bacterial disease. Micrococcus nigro- 

 faciens Nor. (17). Many grubs while active seemed to resist the 

 disease, which attacked a majority of them, but during the quiescent 

 prepupal stage they succumbed. The presence of mites on the body 

 of a grub would often prevent its pupation, or cause the pupa to 

 be deformed, and the adult would not issue. 



TJk first instar. — Technical descriptions of this and the other in- 

 stais aud stages of Phyllophaga vancUnei will be given in a later 

 Issue of the Journal, when detailed studies have been completed. 

 For the present, the plates may be depended upon to give a fairly 

 accurate impression of the size and appearance of the different instars 

 of the grub. 



The average duration of the first instar was determined as 36 days; 

 the maximum, 59 days (in December) ; the minimum, 17 days (\n 

 June). The maxinuun duration was found to be more than three 

 times the minimum. The duration of this, as well as the other in- 

 stars of the grub, has been shown to be influenced more by the amount 

 of moisture in the soil, and by the presence or absence of mites, fun- 



73 



