14 BULLETIN 774, U. S. DEPARTMENT OF AGRICULTURE. 



Myrobalan seedlings. Within the period October 20-November 23, 40 

 oviparous females matured in an average of 19.1 days, the period 

 of development ranging from 16 to 22 days. On Myrobalan plum 

 the development was slightly slower than on Agen (French) prunes. 



Habits and Oviposition. 



The females feed normally on the under surface of the leaves, but 

 occasionally also on tender stalks, especially of sucker growth. The 

 males frequently arrive before the females are mature and settle 

 down beside the immature aphicls. Copulation takes place very 

 soon after the female casts her fourth skin, and a male may copulate 

 with more than one female. As the males are much less abundant 

 than the females this practice is probably common and was often 

 noticed in the cages. Toward the middle of November, 1916, large 

 numbers of immature females were blown off the trees by winds and 

 perished. In some orchards this only thinned out the infestation to 

 a small degree, as plenty of mature females had been observed previ- 

 ous to the coming of the high winds, but in others wherein the sexes 

 were not so advanced it destroyed the majority of the aphids. The 

 oviparous females bear only a scant coat of " meal " and may be 

 easily confused in the orchard with those of Phorodon liumuli 

 Schrank and Aphis cardui Linnaeus, both of which are contempo- 

 raneous with anmdinis. They are less likely to be confused with the 

 plump reddish-brown oviparous form of Bhopcdosiphum nympheae 

 Linnseus. 



As a rule the female commences oviposition within 24 hours of 

 copulation, but this was delayed in some cases as long as 5, and in 

 one instance 10 days. In cages never more than 2 eggs, and more 

 often only 1, were laid in one day by a single aphid. 



Sixteen females laid an average of 4.1 eggs in the period Novem- 

 ber 9-December 18. In the early part of this period the average was 

 6, while toward the end it was 3.5. Not over 7 eggs were deposited 

 by one female. There was a marked tendency to deposit the eggs 

 over a long period — as much as three weeks — and the females after 

 depositing an egg or eggs on the stems generally returned to the leaf, 

 remaining there until the time for the deposition of the next egg. 

 The females usually died within a week of depositing their last egg, 

 but in some cases lived longer, and one aphid lived beyond three 

 weeks. It appeared, however, that those that persisted had not rid 

 themselves of all their ova. as they did not have the shrunken ap- 

 pearance of sterile aphids. 



NATURAL ENEMIES. 



The mealy plum aphis, both on winter and summer hosts, is preyed 

 upon by a large series of natural enemies. As early as March 17, 

 1916, a few eggs of Syrphidae and Chrysopidae were observed de- 



