﻿168 THE BNTOMOLOaiST. 



Temperature and Quickness of Development. 



All breeders of Lepidoptera naturally aim not only at obtain- 

 ing a high proportion of imagines to the number of larvae, but 

 also at obtaining fine richly coloured specimens. No doubt a 

 large variety of factors conduce to the production of such 

 imagines, but one of the greatest is, I believe, quickness of 

 development in the larval stage. Of course, the average life of 

 larvae of different species varies enormously, some taking years 

 to come to maturity and others weeks only ; so that in speaking 

 of quickness of development I only mean it to refer to the usual 

 length of life of the larva under consideration. Suppose, for 

 example, we have a larva whose average life is three months ; it 

 will usually produce a far finer imago, if it comes to maturity in 

 ten weeks, than if it drags on for three and a half months. Other 

 things being equal, the quicker, within certain limits, larvae can 

 be fed up without interfering materially with their cycles, the 

 larger will be the proportion to pupate and the finer the result- 

 ing imagines. This I have found to be particularly the case 

 with larvae that feed up in the spring or early summer. 



Now, if there is one thing that has more influence than 

 another on quickness of development it is temperature. I do 

 not mean by that that the greater the heat the better will be 

 the results. The temperature wants to be consistent with that 

 prevailing under the best conditions at the time of year when 

 the larvae naturally feed ; and, above all, it should be regular. 

 I have frequently obtained quite remarkable results by feeding 

 up certain spring larvae in a temperature of fifty-five to sixty 

 degrees kept up regularly day and night in April and May. 

 This sort of treatment has one disadvantage, and that is that the 

 imagines may appear two or three weeks or more before their 

 proper time ; but against this can be set very many advantages. 

 The larvae seem very much less liable to ailments : they feed 

 heartily and steadily, there is practically no loss in changing 

 skins or pupation, and the imagines are large and handsome. 

 I have found this use of a steady, fairly warm temperature 

 of the greatest help in rearing larvae hatched in the spring from 

 ova which were laid the previous summer or autumn, and have 

 by its means bred without any difliculty several species which 

 pass the winter as ova and are considered difficult, if not im- 

 possible, to get through successfully in confinement. 



Perhaps this effect of a regular temperature is one of the 

 chief reasons why some species vary so enormously in their 

 abundance in different years. If the temperature during the 

 months the larvae are feeding is unusually warm and steady for 

 that period of the year, then the next emergence of the species 

 will be unusually abundant. It will be noticed that I refer to 

 the temperature being warm, not hot. Great heat and drought 



