LIFE-HISTORY OF THE LADY-BIRD BEETLE. 



477 



there is little oi- no migration, that hibernation takes place 

 locally, and that the varieties breed true ? Or, does the particular 

 environment allow only certain varieties to survive ? 



Two, possibly four, factors have to be considered in a genetic 

 study of the Black and Red forms : — 



1. Pattern : that is, the shape and distribution of the spots. 



2. Colour: (a) black, which is the same in both " type " and 



black varieties ; 

 {b) red, which, contrary to accepted opinion, I believe 

 different in the lied and Black forms. 



3. 8ize : there is great range in size in the Coccinellida3, which 



Johnson believes is chiefly adaptational, but the mean size 

 of the varieties under consideration is different, and perhaps 

 constitutes a definite character. 



4. There may be a physiological factor in the reaction of these 



varieties to heat. 



Microscopical examination by transmitted light sIjows that the 

 reddish colour in both varieties is due to a clear yellow, to which 

 brownish-i'ed, semi-transparent particles ai-e added in the Red 

 form and red-brown and carmine in the Black variety. 



There is probably a physiological factor to account for the 

 seasonal appearances of the two forms, in England the Black 

 usually appearing later and disappearing earlier than tlie Red. 

 I have also observed that when the breeding-boxes were over- 

 heated, the Black could live at a higher temperature than 

 the Red. 



2. 77ie Food and Feedinrj of Adalia bipunctata. 



There is considerable difficulty in feeding Adcdia with its food, 

 living aphis. The occurrence of aphis is very erratic, being much 

 affected by sudden climatic changes, such as cold, wind, and heavy 

 rains. At times they disappear inexplicably. 



Adalia will eat many but not all species of aphis. ]^uring two 

 years' breeding I have found three species which are not accept- 

 able : — (1) Aphis ritmicis, the black bean aphis wiiich is found on 

 broad beans in early summer. The young of this species are 

 eaten to a small extent, but the large only under stress of circum- 

 stances. One may continually find a bean-row black with this 

 destructive aphid, but very few lady-birds upon them when, on 

 a bed of nettles a, few j^ards away, can be found large numbers 

 of Coccinellidse — 0. septempitnctaia, C. variabilis, A. bipunctata, 

 Ilalyzia \^-guttata, H. ^l-pnnctaia, and H. li-jmnctata, — even 

 when the aphids are not obviously numerous. (2) A. bluish-green 

 aphis {MacrosipJiuia aconitnm, (Van der Goot)), which I have 

 found only on Monk&lioo<l. This has never been eaten by Adalia. 

 Johnson says "several of the highly-coloured aphis cannot be suc- 

 cessfully fed to Coccinellids." (3) f{i/alopterus primi : this aphis 



