256 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



THE APHIDES ATTACKING CULTIVATED PEAS AND THE 

 ALLIED SPECIES OF MACROSIPHUM. 



By Fred V. Theobald, M.A., F.E.S., Professor of Economic Zoology 

 in London University. 



[Read before the Congress of Entomology at Oxford on August 7, 1912.] 



This paper showed that three species of Aphides or Dolphin attack 

 eiiltivated peas, namely Macrosiphmn pisi Kaltenbach, Megoura viciae 

 Kalt-enbach, and Aphis rumicis Linnaeus. 



The first-named is the most important, and is spoken of in Britain 

 as the green dolphin of peas, in America as the destructive green pea 

 louse. It was originally described by Kaltenbach as Aphis pisi, and 

 was said by him to occur on a number of plants besides Pisum spp., 

 such as Spiraea Ulmaria, Geum urbanwn, Lotus spp., Lathyrus sp., 

 Trifolium spp., Spartium, Ononis, and many others. This pea aphis, 

 the pisi of Kaltenbach, has been sunk as a synonym of Schrank's 

 Aphis ulmariae by aphidologists. Koch described the aphis on Geum 

 as Siphonophora gei, and this has also been sunk as a synonym of 

 ulmariae. 



Mr. Theobald reinstated both Kaltenbach 's pisi and Koch's gei. 

 The characters by which these different green Macrosipha can be identi- 

 fied were shown to be the structure of the cornicles and the arrange- 

 ment of the sensoria on the antennae. 



In Siphonophora pisi the cornicles are imbricated, whilst in S. 

 ulmariae Schrank feeding on Spiraea Ulmaria and in S. gei Koch, 

 which feeds on Geum urbanum, they are reticulated at the apex. These 

 green Macrosipha can be divided into two groups — i., the pisi group, 

 in which the cornicles are imbricated, and this group, also contains two 

 new species, one on Lotus corniculatus — loti Theobald, and another on 

 the wild Trifolium procumhens — trifolii Theobald; ii, contains ulmariae 

 Schrank, gei Koch, and stellariae Schrank, which have the apex of 

 the cornicles reticulate. By noticing these characters we find that 

 M. pisi only occurs on plants of the genus Pisum, Lathyrus (both 

 wild and cultivated), and on all three varieties of clover (Trifolium). 

 This narrows down very much the list of food-plants of this destructive 

 species, and thus gives us more hope of being able to cope with it, an 

 impossible thing to do if it occurred on the great variety of plants 

 m^entioned by previous writers. The life-cycle of pisi was shown to 

 be as follows : The winter in Europe and the northern parts of America 

 is passed in the egg stage on clovers, and to some extent on wild 

 and cultivated Lathyrus (everlasting peas); in May and June winged 

 females fly to the peas (Pisum), and there live until late summer, when 

 they fly back to clovers and wild Lathyri, and also to cultivated ones ; 

 later they oviposit there. 



