SPRING NUMBER 57 
The following data was secured from the breeding work in the 
greenhouse. First, no tendency to oviparous reproduction was 
seen. Both winged and apterous females were produced which 
continued to breed parthenogenetically throughout the winter. 
Second, the rate of parthenogenetic reproduction as tabulated’ 
for all the lines shows that the average age of the mother at birth 
of first young was 11.1 days, average number of offspring 27.7 
and the average length of life 17.7 days. This would allow 
for nearly three generations per month as the maximum rate 
of reproduction. 
The following fall the work of breeding the aphids was started 
again, this time in the open-air insectary. Here the previous 
obstacles were not encountered, and the lines were carried 
through successfully. Three lines were started in November and 
run through the winter under natural conditions. From the tab- 
ulated data we find that the average age of the mother at the birth 
of the first young was 15.4 days, as compared with 11.1 days in the 
greenhouse. We would naturally expect this period to be shorter 
in the greenhouse than outside. 15.4 days would be a fair esti- 
mate of the average length of time for one generation of Myzus 
persicae during the winter months. This would allow for two 
generations of the aphids per month as the average maximum 
number. The average length of the productive period was 18.2 
days, and the total average number of young was 42.8, which 
would make an average of 2.3 per day. The largest number for 
any one day was 8. The average length of the whole life was 36.2 
days. There usually was a period of one to ten days between the 
birth of the last young and death. The nymph molts at the ap- 
proximate ages of one or two days, five days, ten days, and four- 
teen days. A complete tabulation of the data on the life of one 
line shows that three generations usually overlap, also a day of 
high productiveness is usually followed by one of low productive- 
ness, and vice versa. 
The same method of reproduction occurred here as during the 
preceding winter in the greenhouse. No males or sexual eggs ever 
- appeared in the breeding jars. Hence we can conclude that this 
species of aphid lives throughout the year on fresh plants and 
breeds viviparously continuously. 
Parasites and Enemies. In the greenhouse, Myzus persicae 
was very heavily parasitized by the fungus, Entomophthora 
1 The tables are necessarily omitted because of lack of space and only sum- 
maries of the results given. A number of photographs illustrating the thesis are 
also excluded. 
