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A. pisi. The parthenogenetic females are all viviparous ; an adult 

 female can produce from 100 to 150 descendants during its life, from 

 4 to 13 individuals being born daily on blossoming peas and from 

 3 to 10 on clover. The young mature in about 8 to 10 days, accord- 

 ing to the temperature. The amount of food determines whether a 

 wingless individual (when food is abundant), or a winged one (when 

 food is scarce), will be produced. With regard to sexual forms, the 

 author has never found males and females on Pisuni sativum, Vicia 

 cracca (wild vetch) or Lathyrus odoratas (sweet pea), only on Lalhyrus 

 lalifolius, L. ensifolius, Medicago falcata and M. saliva ; these were 

 found during September. These sexual females lay their eggs singly, 

 about 10 in all, on leaves, stems and fruits of Lathyrus, Medicago, 

 Trifolium, Onobrychis and Ononis. 



The subspecies Acyrthosiphon fisi pisi, to which the remarks of the 

 author refer, occurs all over Europe, in Siberia, and the Altai. 

 A. pisi destructor, Johns, is found in the United States and Canada and 

 closely resembles the type form. A. jnsi turanicum, Mordv., found 

 in Transcaspia and Turkestan, is more distinct from it and more nearly 

 resembles A. pisi ussuriensis, Mordv. It is not yet known which 

 subspecies occurs in the Crimea and in the peninsulas of Southern 

 Europe. It is evident that the distribution of these pests has not been 

 assisted by man ; their food-plants (peas, lucerne, clover, sainfoin,, 

 etc.) are grown from seed and therefore eggs laid on plants which are- 

 subsequently mown for hay, would perish. The insects found in 

 European Russia, Siberia and on the Altai do not winter as partheno- 

 genetic females, but as fertilised eggs ; it is not yet known in what 

 stage A. pisi turanicum, winters. The author's studies of the life- 

 history of these Aphids since 1898 in various parts of European Russia 

 have shown that the females lay wintering eggs on some species of 

 Lathyrus, red clover, sainfoin and Ononis ; these eggs produce in the 

 following spring wingless stem-mothers, which develop on the new 

 stems and shoots of these plants. No sexual females breed on Lathyrus 

 odoratus, Pisum sativum, or Vicia cracca ; the last stage on these 

 plants is that of winged parthenogenetic females, which migrate to 

 other plants, where they produce either a new parthenogenetic 

 generation, if it is in summer, or sexual forms in September if on 

 suitable plants. Thus, the development of sexual forms depends not 

 only on the amount of food, but also on some unknown qualities of 

 the food-plant. Aphids breeding on grasses usually appear later than 

 those breeding on trees, which is partly due to the late development 

 of grasses. The larval stem- mothers from the hibernating eggs, pass 

 from the dry leaves and stems to new growth of the same plant or to 

 some annual plant if suitable ones are present. Besides the stem- 

 mothers, which are usually wingless in the case of all Aphids, their 

 first descendants at least are also wingless ; winged individuals only 

 appear later, when the feeding conditions become less favourable ; 

 sometimes, however, even the wingless forms pass from one plant to 

 another in search of more suitable food. Peas are usually attacked 

 in June, the previous generations having bred on Lathyrus, Medicago, 

 Trifolium and other annuals. If the peas have already blossomed, the 

 damage is unimportant. These Aphids remain on peas until the pods 

 have developed ; winged forms then appear. A. pisi is the only 



