HAPLOID MALES ^yy 



cytologically (cf. Schrader and Hughes-Schrader, 1931 ; Torvik- 

 Greb, 1935). 



Table 57 



Examples of Haplo-Diploid Sex Differentiation 



Acarina . Tetranychus himaculaius « = 3 Schrader, 1923. 

 Hemiptera 



(Aleurodidae) Aleurodes proletella . w = 13 Thomsen, 1927. 

 Trialenrodes 



vaporariorum . . n = 11 Hughes-Schrader, 1930. 



(Coccidae) Echinicerya anomala] _ 



Icerya spp. ) ~ " " 



Icerya purchasi (^ and (5*) w = 2 ,, 1927. 



Hymenoptera Apis mellifica . . n = 16 Nachtsheim, 1913. 



Paracopidosomopsis . w == 8 Patterson and Hamlett, 



floridanus. 1925. 



Pteronidea ribesii . n — 8 Peacock and Sanderson, 



1931- 

 Habrohracon juglandis . « = 10 Torvik-Greb, 1935. 

 (also probably in Vespa, Neuroterus and other genera). 

 Rotifera . Asplanchna spp. . . Whitney, 1929. 



The mode of reproduction in Icerya purchasi is exceptional and 

 particularly significant. Fertilised eggs give hermaphrodites. They 

 produce i per cent, of eggs that go unfertilised, and give haploid 

 males, and 99 per cent, that are fertilised either by the sperm of the 

 hermaphrodite or by that of the males. The species therefore has 

 an alternative system of reproduction between hermaphroditism and 

 haplo-diploid sex differentiation. 



Icerya purchasi also has a unique peculiarity in the develop- 

 ment of the testes in the hermaphrodite. The haploid number of 

 chromosomes is found in the spermatogonia, presumably through 

 some process analogous to meiosis having occurred during their 

 development. The testes are, therefore, genetically male, and the 

 " hermaphrodite " diploid genetically female, since it produces 

 sperm only in tissue developed by a special abnormality and 

 genetically that of a different individual. The genetic differentia- 

 tion of haploid and diploid is therefore as sharp as that in the 

 Hymenoptera and the system of reproduction in Icerya is probably 

 derived from the simple haplo-diploid type. 



(h) Hymenoptera. By a prolonged series of experiments, 

 Whiting and his collaborators have discovered the genetic mechanism 



