LÉPIDOPTÉROLOGIE COxMPARÉE 355 



crevices in which to deposit the ova. When once a suitable spot 

 is found, a whole batch of ova is laid bef ore a new place is chosen. 

 The only crossing that is troublesome to secure ova from, is that 

 of hirtaria çj x ponionaria Q. The pomonaria females some- 

 times wander about for days without laying. I persuade them 

 to lay by sealing them in a chip box along wilh a pièce of bark. 

 Ail the others lay very frecly in crevices in chip boxes, m crushed 

 scraps of newspaper or in the folds of the muslin cages. 



Usually, after pairing with maie of hybrids harrisoni or 

 (lenhann, the females lay a few ova and then call for maies again 

 by gently vibrating the protruded ovipositor; in extrême cases 

 they seem to be f atally injured and die at once. Harrisoni females 

 do the same when paired with maies of any species. 



Fertility of first crosses. 



If the pairing has lasted for the normal time, it is quite an 

 ordinary thing for lOO per cent, of the ova to be fertile, except, of 

 course, when either parent is hybrid in origin. Very often in the 

 case of the cross hirtaria cf x zonaria Q, the ova dcvelop for 

 varying stages and then the embryo dies. 



Fertility of second crosses. 



Thèse are generally quite stérile; I once secured one larva from 

 Jiarriscni cf x hirtaria Q , and, from certain broods of hirtaria Q x 

 hunii cf, hirtaria g x pilzii cf, and ponionaria cf x pilzii Q, about 

 3 % of the ova hâve hatched. 



Foodplants. 



Hawthorn {Cratœgus oxyacaniha) is, par excellence, the food 

 plant to use, although birch {Betida alba) and sallow {Salix 

 caprea) are almost as useful. Ail of the hybrid larvas will eat 

 thèse and thrive well but the leaves of most forest trees rre 



