BIOLOGY OF TOBACCO MOTH AND ITS CONTROL 9 



sumed (fig. 1), the method of feeding being similar in some respects 

 to that of leaf -eating caterpillars. 



CANNIBALISM 



When placed in confinement, tobacco moth larvae are cannibalistic. 

 This habit is more pronounced with well-grown larvae, and occurs 

 especiall} T when the victims are weak or inactive from molting or at 

 the time of pupation. The writers have often wondered why the 

 tobacco moth did not increase more rapidly in the large stocks of 

 flue-cured and Turkish tobacco stored in the eastern part of the 

 United States. Although there is the possibility that cannibalism 

 takes place in the warehouses, and that this serves as a check on the 

 multiplication of the species, it was not observed to occur in hogs- 

 heads or bales of tobacco and probably does not exist to any great 

 extent except in heavy infestations. 



RATE OF GROWTH 



The larvae showed a very uneven rate of growth despite efforts to 

 provide uniform conditions of food, temperature, and moisture. As 

 shown in table 1, the period of development may vary as much as 130 

 days in different groups of larvae that hatched in the same week. 



Figure 5. — Full-grown larva of the tobacco moth. X 6. 



The number of molts depends to a large extent on the quality of 

 food and the rate of growth. The usual number is five, but some 

 larvae were observed to molt nine times. The first molt may take 

 place 4 days after hatching, and in the cases observed others occurred 

 at intervals ranging from 2 to 20 days. The molting larvae spin a 

 loose covering of silk in which particles of excrement or tobacco are 

 entangled. In this partial protection the larvae remain while molt- 

 ing, which requires only a few hours under favorable conditions. 



The larva is the most adaptable stage of the moth, it being able 

 to resist starvation for long periods unfavorable for growth, and to 

 change foods with ease, from tobacco to some other dried material, 

 such as dry yeast, cacao beans, unbolted corn meal, or dried butter- 

 milk. The larva was the only stage that passed the winter in un- 

 seated tobacco storages in southern Virginia. In 1932 a total of 433 

 larvae overwintered in the laboratory and the lengths of their larval 

 periods were: Maximum, 354 clays; minimum, 182 days; average. 

 259.7 days. In 1931 the larval periods for 430 overwintering indi- 

 viduals were: Maximum, 336 days: minimum, 209 days; average, 

 261.1 days. The mature larva is shown in figure 5. 



THE PREPUPA 



When larvae are fully grown (fig. 5) they seek a sheltered place 

 for pupation, as explained under adult emergence on page 6. The 



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