before reaching maturity, some from disease or from the artificial 

 conditions of their confinement, others from wrong handling through 

 ignorance of the essentials for their growth. The total number of 

 eggs, larva^, and pupa^ of this species whose molts and instars were 

 recorded was as follows: Eggs, 1,502; grubs in first instar, 852; 

 grubs in second instar, 209; grubs in third instar, 117; pupae, 46. 

 The two charts on Plate VIII show in graphic form tiie length of 

 the egg to adult period of PhyUopliaga vandinei. 



LENGTH OF LIFE-CYCLE. 



The life-cycle of Phijllophaga vandinei covers, roughly speaking, 

 one year. The average normal egg-to-adult period covers just ten 

 months. The average from fourteen complete records of single in- 

 dividuals run from egg to adult was 306 days; the average obtained 

 by adding together the average lengths of the three immature stages — 

 the egg, three instars of larva, and the pupa — was 302 days. The 

 disparity is easily accounted for. 



The maximum egg to adult period of the fourteen individuals 

 was 395 days; the minimum, 212 days. Or in terms of months, they 

 were, respectively, 13 and 7 months. 



Observ^ation has shown that the adult Ijeetle, after issuing from 

 the pupa, may remain in the soil in the pupal cell for a period 

 varying from two weeks to perhaps two months. The period of pre- 

 oviposition of adults was not experimentally determined, because of 

 the refusal of reared specimens to oviposit, and the difficulty of being 

 sure whether specimens collected in the field had just emerged or not. 

 Calculating the pre-emergence period to average a month, and the 

 pre-oviposition period to require close to a month, the species is seen 

 to have a life-cycle of virtually one year. 



Tlie possible shortening or lengthening of the egg-to-adult period 

 by three months, which was demonstrated in rearing boxes, and 

 whicli would shorten or lengthen the entire life-cycle by an equal 

 period, gives the life-cycle of the species a proven variation of nine 

 to fifteen months. This might be still further lengthened by the fact 

 that the egg-laying period of the female may extend over a period 

 of more than a month. 



It is very conceivable that an egg laid quite late in the fall might 

 not. under adverse conditions, emerge as an adult until tlie spring of 

 the second year following; or on the other hand, that an egg laid 

 in spring might, under very favorable conditions, produce an adult 

 in the fall of the same year. This last, in fact, happened in one of 



71 



