THE MEALY PLUM APHIS. 7 



usually deposit young within a very few hours after shedding the 

 final skin. 



A minimum -generation series of last-born aphids is indicated 

 below : 



Table III. — Development of minimum-generation series of the mealy plum aphis. 

 Walnut Creek, Cal., 1916. 



Genera- 

 tion of 

 individ- 

 ual. 



Date of 

 birth. 



Date of 

 fourth 

 molt. 



Develop- 

 mental 

 period. 



I 





Mar. 31 

 May 3 

 June 11 

 July 12 



Days. 



II 



Ill 



IV 



Apr. 21 

 May 29 

 July 1 



12 

 13 

 11 



These four generations were completed in about four months, or 

 over a month longer than the seven generations of the first-born 

 series. 



The period of reproduction as indicated in the foregoing table 

 varied from 20 to 26 days. 



Repeoduction. 



Observations were made on the reproduction of individuals of 

 wingless generations 2 to 5 inclusive. Adults of the second genera- 

 tion, for a total reproductive period of from 4 to 5 weeks, averaged 

 about 4 young daily, producing the first three weeks a daily average 

 of 6 young. The later generations were less prolific, fourth and 

 fifth generation individuals not averaging above 2£ young per day. 

 Ten young were deposited within 24 hours on several occasions, but 

 on no occasion was this number exceeded. The rise and decline in 

 fecundity was in the main similar to that found in the case of the 

 stem mother. 



Habits of Spring Generations. 



The aphids of the second generation, when newly born, dispose 

 themselves in groups, close by the parent, on the underside of the 

 leaf. After the first molt many remove to other leaves and this is 

 the beginning of the migration from leaf to leaf and branch to 

 branch. Second-generation larvae and adults prefer to suck the 

 rib tissues of the leaf. Owing to the rapidity of reproduction and 

 consequent crowding, the aphids of later generations have little choice 

 of location and feed at any point on the lower surface of the leaves 

 or on petioles. If the lower surface of a leaf is entirely occupied 

 many larvaa will be found feeding on the upper surface, in some 

 cases apparently in preference to seeking other less crowded leaves. 



