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ENTOMOLOGICAL SOCIETY 



molts of the same individual varies greatly; not as much, 

 however, as it does for different individuals. The following 

 table shows these variations, each individual being subjected 

 to the same conditions. Nos. A to E represent different 

 individuals. 



Variation in the duration of the different instars in Toxoptera gram- 



inum. 



There is also great variation in the time from the birth of 

 individuals to the fourth molt and the appearance of the first 

 young, as will be seen from the following table. Individuals 

 in this table are same as in the preceding, with the addition 

 of F and ib 3 . 



Variation in the time from birth of individuals to fourth molt and 

 appearance of first young, in Toxoptera graminum. 



From the above data it seems that there is no fixed period 

 for the different molts or the appearance of the first young. 



It was found that a temperature of 30 F. or below had 

 the effect of lengthening the period between molts; also, of 

 lengthening the period between generations. At the ordinary 

 summer temperature, a generation is produced in from 6 to 

 ii days; in autumn the period varies from 14 to 48 days. A 

 temperature of 8 F. does not kill the insects, but as soon as 

 the temperature rises to from 40 to 50 F. they go on re- 

 producing. 



