64 



Notes on the genus Zygaena. 



By T. H. L. Grosvenor, F.'E.S.—Reacl December IQth, 1922, 



I must apologise for the obvious shortcomings of this paper. 

 When invited to do something with reference to the Zygaenas, I 

 had a faint hope that something of interest might be written, as I 

 had at least 2,000 larvae, all bred from selected parents and carried 

 to the second generation. Circumstances, however, have decided 

 otherwise, for out of all those larvae I only bred about two dozen 

 imagines, the remainder dying as pupae. Instead of the imagines 

 developing they rotted, and the pupae were filled with a black fluid, 

 so that one was unable when opening them to obtain the results, 

 and, from a Mendelian point of view, all one can say is, that the 

 black and yellow forms follow these lines. Confluence, which will 

 be dealt with later, apparently does not follow any rule. 



The result of pairing black and red, and yellow and red, always 

 produces in the first generation 100% of the type; a pairing of these 

 types produces a percentage of the aberration, but on this occasion 

 the results obtained were too small to give any definite figures, and 

 the only pairing obtained of black x black was infertile. Newman, 

 who has bred the yellow form in large numbers, shows that this 

 follows Mendelian lines, and he has obtained pairings, yellow X 

 yellow, which produce 100% of yellow. 



In regard to confluence, one is of opinion that this result is caused 

 either by temperature or atmospheric conditions, with a greater or 

 lesser tendency in various colonies to produce this form. One has 

 on many occasions bred Z. trifolu from selected parents with the 

 following results. A pairing of two of the most extreme confluent 

 forms, in the first generation produced the type, i.e., with spots 1 

 and 2 separate, 3 and 4 connected, and 5 free; there were also a 

 few of the form orobi. The result of several pairings from these 

 produced an overwhelming number of orobi, i.e., with spots 3 and 4 

 disconnected, but not a confluent form was obtained. On the other 

 hand confluent forms may be obtained from any pairing, generally 

 in the first generation, the greatest number obtained from any one 

 pairing was from a brood, type x black, which in the first genera- 

 tion produced about 27 typical and ab. orobi, and 11 showing vary- 

 ing degrees of confluence. From observations made over several 

 years, confluence appears to be caused by similar conditions to those 

 which produce blueness in the females of the Lycaenidae. 



