228 Variation in the Mealworm, Tenebrio molitor 



In genetic investigations made on Tenebrio molitor the occasion 

 presented itself for making various observations of a more biological and 

 systematic nature. Some of these are ripe for communication. Of the 

 genetic investigations a more detailed report will follow later on. 



A. The Larva. 

 1. Colour. 



When observing a population of Tenebrio larvae, furnished by the 

 trade, one will in most cases be struck by the fact that the colour of 

 these larvae is very variable. If the culture under observation embraces 

 a large number of individuals, two markedly distinct colour-types may 

 nearly always be isolated, viz.: 



a. Larvae of a light orange red colour, which will henceforth be 

 called the OR larvae (orange red). 



6. Larvae in which the orange red is replaced by a dark chestnut 

 brown, designated by the name of the GB larvae (chestnut brown). 



If fortune favours us, a third type, as an exceptional case, may be 

 observed, viz. larvae that are still darker (sometimes considerably darker) 

 than the CB larvae, and which, on account of the jet black colour of the 

 ventral abdominal segments of the adult beetle, will be distinguished 

 from the two others as the BA larvae (black abdomen). 



Besides these three types, one will meet with a large number of 

 intermediate colours in which the orange red may be blended with the 

 chestnut brown so as to produce many shades of reddish brown and 

 brownish red. 



The BA larva is very rare and is not so easy to isolate as a pure 

 strain as the OR or CB larvae. 



This third type (BA) will be referred to again in the discussion of 

 the beetle. For the moment we shall confine our attention to the OR 

 or CB larva which are easy to distinguish. 



When from these isolated types some generations are bred, they 

 prove to be (with respect to their colours) homozygous races whose cross- 

 breeding produces, in the F^ generation, the immediate colours referred 

 to above. 



At first I thought that the CB larva was identical with the larva of 

 T. obscurus, and the OR larva with T. molitor. 



In the extensive literature on Coleoptera the larva of T. obscurus is 

 designated as dark brown in contradistinction to the larva of T. molitor, 

 which is described as being red. Curtis gives of the larva of T. obscurus 

 a coloured picture corresponding entirely to the CB larva. Besides one 



