26 PARTHENOGENESIS. 



may be mentioned Nematus fallax, yet on counting the 

 specimens which I have caught and bred, I find a pro- 

 portion of about one male to twenty females. 



The number of species in which no males are known 

 is pretty considerable, yet as many of these are rare 

 and local, it cannot be said with certainty that they do 

 not exist. Yet with some common species there is 

 evidence tending to show that this is actually the case, 

 or if they do appear it is at rare intervals. For 

 instance, Mr. Smith bred one year about four hundred 

 females of Eriocampa ovata, while not one of the other 

 sex made its appearance. This is also my own 

 experience ; nor has any Continental author described 

 it. Again, I have frequently bred such abundant 

 species as Hemichroa rufa, Phyllotoma nemorata, 

 Poecilosoma pulveratum, Fenusa betulce, without males 

 coming forth, and this has been the case with many 

 other observers. 



Dineura verna is a widely known and common species, 

 of which no males have been discovered ; the same may 

 be said of Poecilosoma luteolum,* Hoplocampa brevis, 

 Blennocampa brevis, B. luteiventris (?), I?, albipes, Ne- 

 matus Erichsoni, and N. pallidiventris. The lack, or at 

 least extreme scarcity, of males in these insects may be 

 accepted with tolerable certainty, since, if they existed 

 at all they would, ere this, have been bred. And, as 

 every breeder of insects knows, males are easier to rear 

 than females, from their smaller size and from their 

 appearing earlier. 



But the evidence of the occurrence of partheno- 

 genesis with the Tenthredinidce is not altogether of this 

 negative nature. From the admirable and thorough 

 observations and experiments of Kessler (Die Lebens- 

 geschichte von Ceuthorhynchus sulcicollis und ISTematus 

 ventricosus, Cassel, 1866), and more especially of von 

 Siebold (Beitr. zur. Parth. d. Arth., pp. 107130), 

 there cannot be the slightest doubt that Nematus ribesii 



* Andre has recently signalised a male of this species from Syria, the 

 only record I have of its existence (Ann. Soc. Ent. Tr., 1881, 353). 



