528 MR. L. DONCASTEU ON COLOUR- VARIATION [DeC. 12, 



5. On the Colour- Yariation of the Beetle Gonioctena 

 variabilis. By L. Doncastee, M.A., F.Z.S. 



[Received July 7, 1905.] 



In 1895 (P. Z. S. 1895, p. 850) an account was given by Mr. Bate- 

 son of the colour- variation of Gonioctena variabilis, a Ghrysomelid 

 beetle. His material was collected almost entirely at Granada 

 in the months of March and Ay^il ; and he found that although 

 the insect is extraordinarily variable, yet when a large collection 

 is made the beetles could be classified into two chief groups with 

 very few intermediates between them. The gTound-colour of 

 the elytia varies from a biilliant red through orange and buff to 

 a gr-eyish green ; and although the intermediate colours (orange 

 and bufi") are comparatively rare, no sharp line between the red 

 and green can be drawn. Thei'e is also a great diversity in the 

 markings : some individuals, chiefly those with red elytra, have 

 two black spots on each elytron (spotted type), others (almost 

 exclusively greens) are without these spots but have rows of 

 minute black dots (striped form), and a third class has both spots 

 and stripes. A large series of figures is given in the paper 

 referred to. Bateson further found that the spots and stripes 

 have a definite relation to the sculpturing of the elytra ; the 

 spots having their centres on certain of the longitudinal rows of 

 punctulations, while the stripes lie between them. The spotted 

 or striped type may be associated with either the red or green 

 colour, but Bateson observed that almost invariably the spotted 

 elytra were associated with black pigmentation of the ventral 

 surface of the abdomen, and that specimens with no spots had 

 no black pigment in this position. The colour of the underside 

 therefore provided a means of dividing a population into two 

 classes with exceedingly few intermediates ; some had dark 

 undersides and spotted elytra (with or Avithout stripes in addition), 

 the remainder had light undersides and were without spots. 

 "When classified in this way, it is found that most of the dark- 

 spotted specimens have red or reddish elytra, and most of the 

 unspotted light are green ; and further, that about 80 per cent, 

 of the first class are males, and about 70 per cent, of the second 

 class females. The males are easily distinguished from the 

 females by the presence of a small rounded depression in the last 

 uncovered abdominal plate ; this is absent in the female. 



In addition to the variations mentioned, there may be more 

 or less suffusion of the elytra, with black pigment, until a totally 

 black form is reached. The siDecimens in which this melanic 

 variation is not very jaronounced show that they belong to the 

 class which is both spotted and striped ; it occurs much more 

 frequently in red than in green individuals. 



