25 



LENGTH OF LARVAL STAGE. 



Most of the observations upon the larval stage were made between 

 September 1 and December 15, 1902. The temperature prevailing dur- 

 ing the first half of September was as high as is ordinarily experienced 

 at Victoria during midsummer, and therefore the extremes of the 

 average season may be considered as having been covered. 



The time of egg deposition was easily determined by exposing unin- 

 fested squares in breeding cages containing active females. The time 

 of hatching of the larva could only be found by opening the square, 

 and it was so ascertained. The newly hatched larva was then placed 

 in a small cavity made by lifting the covering on the side of a freshly 

 picked square and removing one or two of the immature anthers. 

 The coverings were then replaced as carefullj 7 as possible. Another 

 disturbance was necessary to determine exactly the date of pupa- 

 tion. Observations made in this way were checked by others using 

 larvse which were allowed to go from egg deposition to pupation 

 under natural conditions and without disturbance until the end of 

 the larval stage was approximately reached. Since the sum of the 

 times found for the various stages agrees approximately with the 

 known length of the immature period in cases where no disturbance 

 of normal conditions occurred, we may conclude that the periods 

 found for the larval stage were approximately correct. 



Altogether 266 observations were recorded upon the length of this 

 stage. The majority of the observations may be included in three 

 groups, and when thus grouped they may be best considered in relation 

 to the effective temperature. Table III presents a brief summary of 

 these groups: 



Table III. — General results as to length of larval stage in squares. 



Period of examination. 



Mean 

 average 

 temper- 

 ature. 



Average 

 effective 

 temper- 

 ature. 



Number 

 of obser- 

 vations. 



Average 



range of 



stage. 



1902. 

 September 6 to October 5 . 



°F. 

 78.7 

 73.6 

 62.5 



°F. 

 35.7 



30.6 

 19.5 



195 

 15 

 15 



Days. 

 6 to 9 



September 26 to October 21 . 



7 to 12 



November 11 to December 12 . 



20 to 30 







During the heat of summer the larval stage requires approximately 

 one week. This time appears to hold so long as the mean average 

 temperature remains above 75° F. As the temperature falls below 

 that point there is a gradual increase in the length of this stage. The 

 average total effective temperature required during hot weather by 

 the larval stage is not far from 280° F. As development becomes 

 retarded by colder weather the average total effective temperature 

 required to complete it is much greater. 



These facts may be expressed in general by stating that during the 

 hottest summer weather the length of this stage is somewhat less than 



