68 Inheritance of Melanism in Tephrosia (Ectropis) 



the mortality rate. Still it was finally by manipulating the food plant 

 that success was obtained. Once, after removing the larvae from the 

 airtight tin boxes in which they passed their first (and occasionally their 

 second) instars on a hawthorn diet, influenced no doubt by the incon- 

 gruity of the name " histortata " for an insect which prefers Larix 

 decidua and Betula alba and also by the fact that odd larvae placed on 

 Cyclamen persicum thrived amain, I placed various batches on Poly- 

 gonum^ aviculare, Primula^ acaulis and Primula auricula. In all three 

 cases the larvae did splendidly, but as Polygonum aviculare was the 

 easiest plant to obtain in quantity it was subsequently always utilised in 

 experiments with Tephrosia ; no matter whether T. histortata, T. crepus- 

 cularia, or any of their multitudinous hybrids, are being reared I always 

 commence them on Crataegus and finish on Polygonum aviculare. 



Further trouble developed when cross-pairing was to be attempted, 

 as a very effective barrier to its occurrence was encountered in the 

 difference in time of appearance of the two species; T. histortata 

 '(double-brooded) emerges in March and April, whilst T. crepuscularia 

 (single-brooded) is on the wing in May and June. Fortunately enough, 

 to counteract this turned out to be an easy matter ; all that proved 

 necessary was the removal of T. crepuscularia pupae (wintered outside) 

 to an unwarmed room in late February until the emergence of the 

 first imago. As soon as that took place the T. histortata cages had to 

 be brought alongside them. Then that species commenced to come out 

 at once since, like many other Spring Lepidoptera, they await the 

 stimulus of rising Spring temperatures as fully formed imagines within 

 the pupal shell for considerable periods before their escape; thus no 

 delay is occasioned during histolysis and histogenesis. 



Cross-pairing the resulting moths was an easy matter ; mere con- 

 finement of the opposite sexes in small muslin cages for one evening 

 sufficed to secure its success. However, one's difficulties did not end 

 with successful matings. If the fertile females were not provided with 

 roughened narrow crevices into which to thrust their ovipositors other 

 sources of trouble cropped up. Oviposition in this pair of species 

 apparently occurs in response to the stimulus of what Loeb would call a 

 stereotropism. Hence, to ensure an abundance of ova, the cages must 

 be provided with pieces of bark, crushed tissue paper, and the like. 

 Even then failure is certain if the cages are not handled as little as 



1 The genera Primula and Cyclamen belong, of course, to the same Natural Order 

 Primulaceae, and Polygonum avinilare and Polygonum bistorta are obviously both members 

 of the order Polygonaeeae, 



