Raymond V. Wadswortii 205 



and proceeds to make a meal of it. In one instance, the writer kept 

 larvae fed only on Ephestia and Tortrix, for some six weeks. They 

 accepted the diet and outgrew other larvae hatched at the same time 

 and fed on dried beetroot — a favourite food. It thus seems that the 

 larva is fairly broad in its food list, and is unfortunately no epicure. 

 This of course increases the seriousness of the pest, and makes its exter- 

 mination more difficult. The larva will change its diet fairly readily; 

 from a hard food to a soft food it will change with ease and rapidly 

 settle down, but rice versa, though ultimately it will become accustomed 

 to its new food, it will wander far in search of something more to its 

 liking. 



The length of life of the larva is generally accepted as being about 

 ten to twelve weeks, but very varying lengths have been given by differ- 

 ent authorities. Sharp gives ten weeks or even less, whilst Durrant gives 

 as long as eighteen weeks. The difference arises from the effect of food 

 and temperature. Sharp says, "The enormous increase being due in all 

 probability to the fact that the favourable conditions and equable 

 temperature in the mills promote a rapid succession of generations." 

 It would be well to add favourable food to the above conditions. 

 Under tliese circumstances there can be as many as six generations in 

 the year, but under more natural conditions the number of generations 

 can be reduced to one per annum. Even however given constant con- 

 ditions of food and temperature, some larvae will grow very much more 

 quickly than others. Often, larvae will in six weeks reach twice the size 

 of others hatched at the same time. This happens more obviously under 

 poor conditions than under good ones, and of course means the necessary 

 overlapping of generations. The writer has found that very hard foods, 

 such as dried potatoes, will abnormally prolong the life cycle, so that 

 not even one generation is produced in a year. In ordinary circumstances 

 dried potatoes are practically never attacked, even though presenting 

 ideal conditions. 



When the larva is full fed, it leaves its silken case and the food on 

 which it has been feeding and goes in search of a safe place in which 

 to pupate. Very seldom indeed does it pupate where it feeds. It is at 

 this stage that the presence of the larva is very noticeable. The bags 

 and walls become covered with silken threads, and numbers of fat and 

 well-grown larvae are to be seen wandering over floors and walls and 

 bags. This exodus in a cool store takes place in August and September, 

 but in hot stores takes place more or less all the time. After some days' 



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