62 THE EEPORT OP THE No. Sft 



The Stem Mother. 



The newly hatched, dark green stem mothers migrate to and settle on the 

 buds, where they feed on the green tissue. Later on, they attack the tender 

 leaves and blossom buds. After moulting four times, they reach maturity in. 

 four or five weeks and commence within a day or two to give birth to living 

 young. The first young are produced about the time the most advanced blossoms 

 open. 



Description. The adult stem mother is a glossy black, globose insect,, 

 about 8.07 mm. x 1.44 mm., with 5-jointed antennae. 



Breeding Experiments. 



In our insectary experiments with 15 individuals the following data were 

 obtained : — 



Number of instars: Eive.* 



Length of Nymphal Life: Maximum 37 days, minimum 30 days, average 

 31.8 days. 



Age when reproduction commenced: Maximum 37 days, minimum 30 days^ 

 average, 32.6 days. 



Reproductive period: Maximum 41 days, minimum 26 days, average 32.9 

 days. 



Fecundity: Greatest number 198 young per insect, smallest number 80" 

 young, average number 154.9 young. 



Daily production of young per female: Maximum 18 young, minimum 1 

 young, average 4,8 young. 



Tot^l length of life: Maximum 85 days, minimum 57 days, average 69.5 days. 



Summer Forms on Cherry. 



The progeny of the stem mothers develop into apterous viviparous females. 

 This generation is then followed by brood after brood of wingless and winged 

 aphids. The apterous forms remain on cherry and may be found on this tree 

 from spring till late autumn. The alatse on the other hand leave the cherry 

 and migrate to Lepidium. 



Apterous Vivipara. 



During the early part of the season wingless forms are very common but 

 as the summer wears along they diminish in numbers. This decrease is due 

 to the production of alatae, to the effective work of predaceous enemies and also 

 to the drying up of the affected foliage. Moderately infested trees are liable 

 to support more apterous lines throughout the season than are heavily infested 

 ones. In fact, on badly attacked cherry trees the aphids may wholly disappear 

 by mid-summer. For example; in 1915, in a seriously infested orchard at Vine- 

 land, no plant lice were found on the trees after mid-August. 



Description. The adult wingless vivipara like the stem mother is globose 

 and glossy black. IJnlike the latter, however, it possesses 6-jointed antennno. 

 In size, it is about 2.16 mm. x 1.17 mm. 



*In order to avoid repetition T might mention here that all the other forms have 

 five instars. 



