6 BULLETIN 90, U. S. DEPARTMENT OP AGRICULTURE. 



winter, sexual forms and eggs of this species are not produced, at 

 least until parthenogenetic reproduction causes deterioration. 1 



In other parts of this country where the winter conditions are more 

 severe the rose aphis passes the winter in the egg stage. At Wash- 

 ington, D. C, on November 29, 1912, the writer found a few eggs 

 of this species laid on the twigs of rosebushes. These small, oval, 

 shining black eggs were fastened to the sides of dormant buds. 



Buckton 2 described the eggs as follows: 



The eggs are at first yellow, but subsequently they become black by reason of 

 certain changes shown by Balbiani to result from fecundation. Previous to this time 

 the outer coats are sufficiently thin and transparent to allow the process of segmentation 

 to be observed. 



Notwithstanding the great size of the ovum the female may carry five or more. 

 These, however, are not equally large, but are found to vary in bulk as they approxi- 

 mate maturity and the time for expulsion. 



In California during the fall and spring, while the rose shoots are 

 growing vigorously and producing much tender growth, the rose 

 aphis reproduces very rapidly. During the summer, however, the 

 rate of reproduction seems to be much reduced, and, owing to the 

 attack of natural enemies, this insect does not greatly increase. 

 In the winter the time of development is lengthened and the rate 

 of reproduction is considerably less. 



During the months from October, 1909, to March 10, 1910, the 

 author endeavored to ascertain the number of young produced and 

 the average rate of reproduction under normal conditions. This 

 was done by marking rose twigs having a single female and, after 

 examining them every other day, removing all the young born at that 

 time. Thus the aphides were exposed to temperature, rain, and 

 all other natural conditions which might influence them. Under 

 this method many females were knocked from the bushes and lost, 

 but as this would occur naturally it demonstrates fairly well the 

 average rate of reproduction, if not the maximum, under the condi- 

 tions most favorable for the adult. These records have all been 

 included in Table I. 



1 B. M. Lelong, in the Report of the State Board of Horticulture for California, for 1889, page 213, states 

 that " Kyber, in 1815, has had the rose aphis producing young for four years. From his carefully conducted 

 experiments and from corresponding ones made by other naturalists a law has been educed, which we dare 

 not destroy, ' that under certain circumstances, a female aphis may without coupling continue propagating 

 to infinity, provided that the necessary conditions for the development of the young — food and heat — are 

 not wanting.' " 



s Buckton, G. 15., Monograph of the British Aphides, vol. 1, p. 107-108, 1875. 



