Biological Papers. 



317 



to reproduce the young were removed every day at noon. Careful 

 maximum and minimum thermometer records as well as moisture 

 records were kept during the entire experiment. 



It was found that one aphid at a mean daily temperature of 63.4 

 degrees F. and in a mean daily moisture of 79.1, reached maturity 

 in 16 days, with 14 and 28 days as extremes. Average number of 

 young per day, 1.7, with an average of 76 during the reproduction 

 period, with 26 and 108 as extremes. Average length of life, 60 

 days, with 41 and 86 as extremes. 



RELATIVE RATE OF INCREASE, 



The preceding data show the average period of reproduction of 

 Siphonophora ros(2 to be 43 days, with an average daily reproduc- 

 tion of 1.7. The young at the end of 16 days also begin to repro- 

 duce. It is now readily found that the progeny of a single aphid 

 at the end of 48 days will be 1201 agamic females. 



The average length of time for the parasite to pass from egg to 

 adult has been found to be 16 days, and one fertilized female of 

 Lysiphlehus cerasaphi.H successfully parasitized an average of 70.8 

 lice, 70 per cent, of which were females. From this it can be 

 readily calculated that the total progeny at the end of 48 days or 

 third generation would be 177,261 individuals. Theoretically the 

 progeny of one parasite at the end of 48 days would be able to kill 

 the progeny of 140 lice living under the same conditions. 



The fact that this parasite seems unable to utilize other lice as 

 hosts will not operate seriously against its usefulness as an enemy 

 to the "green fly," for the reason that the green fly passes the whole 

 year on rose plants and is a host always available. 



It seems altogether probable that in this parasite we have an 

 efficient enemy of the green fly, and possibly a method of control- 

 ling this one of the most serious insect enemies of the rose grower. 



