BR. I. ENT. NAT. HIST., 7: 1994 



BREEDING EURODRYAS AURINIA ROTT. AB. VIRGATA Mil 



Rupert Barrington 

 101 Egerton Road, Bishopston, Bristol, Avon BS7 8HR. 



E. aurinia ab. virgata is characterized by having the central row of upperside 

 forewing black spots greatly reduced or absent, leading to the pale markings extending 

 to form a pale median fascia (Porter, 1989). It is a form that probably occurs from 

 time to time in most colonies of this species, although extreme forms are rare. Some 

 colonies, however, have produced well-developed forms on a regular basis. Hod Hill 

 in Dorset was, in the past, one such locality. 



In the field transitional forms from type through to extreme virgata may be found, 

 which would suggest that this is an example of multifactorial/polygenic variation. 

 In this type of variation 'a number of different genes may have similar effects and, 

 should they act cumulatively, they may give rise to a graded series of varieties in which 

 distinct segregation cannot be recognised' (Ford, 1945). This is as opposed to recessn e, 

 dominant or semidominant aberrations in which a single mutant gene is responsible 

 for the variation, and will, when bred, 'produce two or three clear cut classes' (Berry, 

 1977) of aberrations in the subsequent generations. 



It appears that the terms 'multifactorial' and 'polygenic' (and hence 'single-factor' 

 and 'monogenic' when discussing single mutant genes) are synonymous, as various 

 authors have used one or the other to describe the same phenomenon. Multifactorial 

 is used by Ford (1945) and Berry (1977), whereas Ford (1964), Robinson (1971) and 

 Robinson (1990) use polygenic. Kettlewell (1973) uses both as a heading to his 

 paragraph on this form of variation. 



In June 1990 a worn male virgata was taken in Dorset. This was placed in a cage with 

 a fresh, wild-captured typical female, and a pairing was soon observed. As the male of 

 this species leaves a permanent plug after mating to ensure that the female will not pair 

 again, it was certain that the female had not mated previously. Two batches of eggs were 

 laid and a brood of approximately 120 adults reared the following spring. This contained 

 two male virgata (not extreme), and a small number of transitional forms in the male. 

 All females were of the typical form, as were the rest of the males. A pairing was obtained 

 between a transitional male and a typical female. The weather at this time was cold and 

 windy, and the female waited 7 days before pairing. A single batch of eggs was deposited. 



In the spring of 1992 about 100 larvae emerged from hibernation, but they were 

 weak, and many more succumbed to disease than is usual in this species. About 50 

 adults emerged. The whole brood was graded from type to fully developed virgata 

 in both sexes (a male is illustrated here). Expecting pairing to be as easily achieved 

 as is usual with aurinia, a number of the most extreme adults were placed in breeding 

 cages, but despite continuous warm and sunny weather no pairings were observed 

 and no eggs laid. The brood was weak, with a number of deformed adults and some 

 that were unable to hang onto the netting of the emergence cage for long enough 

 to allow full expansion of the wings. 



The graded nature of the brood supports the suggestion, based on fieldwork, that 

 this variation is multifactorial/polygenic, and it clearly has a weakening effect on 

 the aberrant individuals. This is very much in line with the classic study of a colony 

 of aurinia near Carlisle over a period of 55 years as described by H. D. and E. B. Ford 

 (1930) and summarized by E. B. Ford (1945). Here variation increased dramatically 

 when the population rose sharply from a period of scarcity, and many of the 

 aberrations were weak or deformed. They described and illustrated an aberration 

 (virgata) which appears to have been the most frequent form of variation in this colon) 



