THE EOSE APHIS. 9 



Of four other aphides, born on October 10, two became adult and 

 gave birth to young on October 22, or in 11 days, while axiother 

 required 12 days, and the fourth 13 days. 



Another aphis was born on October 19 and emerged as a winged 

 female on November 3, reaching maturity in 15 days. This insect 

 lived as an adult for 17 days and gave birth to living young for 14 days. 

 During this time she gave birth to 87 young, or an average of 6^ per 

 day. During this time the average mean temperature was 67° F. 



LIFE CYCLE IN CALIFORNIA. 



During the winter months of 1909-10 the life cycle was observed in 

 California in a number of cases. Aphides born on the 18th of Novem- 

 ber became adult wingless females and began to reproduce young in 

 from 15 to 18 days, and in two cases the offspring of these same insects 

 became mature and began to reproduce in from 18 days for wingless 

 females to 21 days for winged females. Aphides born November 26 

 emerged from nymphal skins as winged adults in from 23 to 25 days. 

 Thus the wingless forms developed in all cases from 7 to 8 days sooner 

 than winged forms. 



This was the maximum life cycle, and during the rest of the year 

 the growth must have been much faster, but observations were not 

 made owing to press of other matters. 



GENERATIONS. 



Taking 25 days as a maximum, this would allow more than 12 

 generations annually, but with the shorter life cycle required during 

 the warmer part of the year this number must be exceeded by at least 

 7 or 8 generations. In greenhouses there are probably 25 to 30 

 generations in a year. 



LONGEVITY. 



During the winter these insects are long lived for such delicate 

 creatures. One lived under the direct observation of the writer for 

 40 days and another for 33 days. Probably this is longer than for 

 the same insect the rest of the year. 



NATURAL CONTROL. 



RAINS. 



In southern California the rainy season extends from about October 

 1 to May or June. Usually before the rains set in the weather becomes 

 cooler, but the rains are not as a rule hard and dashing, as are those 

 so fatal to aphides in the East, and this apparently explains their 

 slight effects as observed on the rose aphis. Undoubtedly some are 

 washed away and destroyed by rain, but not to the extent occurring 

 in the East, although reproduction seems to be greatly checked during 

 a rainstorm. In the East this insect is many times nearly extermi- 

 nated by a hard, dashing rain. 



