812 Sexual Forms o/Apliis saliceti, Kalt. 



so far as is known, is likewise a raonophytophagous species of the willow, 

 may sometimes produce its sexuales in June ; and if this should prove to 

 be the case, it would be an interesting point that two species of different 

 genera on the same host plant should both produce their sexuales at this 

 unusual season. The sexuales of Melnnoxanthus have not been described, 

 though Mordwilko {Biol. Centralbl., 1907, p. 533) says he found them in 

 August and September. The life-cycle of this species requires further 

 investigation. 



Parallel instances of the appearance of the sexuales in the summer 

 are rare. Buckton {Moyiograph of British Aphides, ii., p. 149) records 

 that he found the sexuales of Macrosiphum tnuralis on Laciuca in the 

 first week of July, but the females had then no eggs ; and Koch says that 

 the males of Myzus persicae occur in May, but, as Buckton and other 

 observers have found the sexuales of this species in the autumn, it is 

 possible that Koch's identification was incorrect. These seem to be the 

 only similar cases on record; but it is possible that, with further study 

 of the life-cycles of different aphides, the appearance of the sexuales in 

 summer will prove to be more frequent than is now supposed, and that 

 the disappearance of some forms, which is at present attributed to the 

 migration of a biphytophagous species to the second host plant, will 

 prove to be part of the normal cycle of a monophytophagous species after 

 the production of fertilised ova. If so, as is actually the case with Aphis 

 saliceti, the race can have at most but two or three months of active life : 

 the rest of the year it exists in a dormant condition as an egg. 



This species is dimorphic in respect of the parthenogenetic genera- 

 tions. The colour ranges from dark green to orange brown with inter- 

 mediate varieties. This dimorphism extends to the sexuales, but here 

 I found that the predominant colour for males was brown, and for 

 females green. 



The male. 



Apterous. Short, oval. Length = -92 mm. Breadth of abdomen = 

 •50 mm. Head, dusky. Eyes, reddish brown. Total length of antenna = 

 1-00 mm., colour, dark brown, with numerous small supplementary sen- 

 soria on segments III, IV, V. Thorax and abdomen, orange brown (rarely 

 green), with a few darker markings on the dorsum. Genital })lates dusky. 

 Cauda, pale brown (or green). Cornicles, pale brown (or green), with 

 dark imbricated scales, length ^ -28 mm. Legs, pale brown, very long 

 and stout, with stiff hairs on femora and tibiae. Tibial joints and tarsi 

 dusky. 



