CONTROL OF INSECTS ATTACKING STORED TOBACCO 



9 



hibit a wide variation in rate of development during the warm months 

 of the year, and this is the only stage of the insect that passes the 

 winter in hibernation. Under favorable conditions of growth the 

 larval period in tobacco averages about 35 days during the summer 

 months. 



At the completion of growth the larvae seek a sheltered place for 

 pupation, near the surface of the tobacco or in some other location in 

 the storage house. They spin loose cocoons and transform into light 

 brown pupae. The length of this stage is about 10 days in summer 

 and about 17 days in spring and fall.. The four stages of the tobacco 

 moth are shown in figure 5. 



SEASONAL OCCURRENCE 



The tobacco moth passes the winter as a larva in hibernation. 

 The overwintering larvae range in size from one-fourth to full 

 grown, and in the fall many of the mature individuals migrate from 

 the tobacco to sheltered places about the building, where they spin 



Figure 6. — Seasonal occurrence of the stages of the tobacco moth in Virginia and North 

 Carolina, based on laboratory life-history studies and on observations made in tobacco 

 warehouses from 1932 to 1934. 



loose cocoons of silk, in which they hibernate. The immature larvae 

 as a rule remain in the tobacco in an inactive condition during the 

 winter, and their populations are not reduced materially by the winter 

 temperatures prevailing in Virginia and North Carolina. The full- 

 grown larvae start pupating in March, and the moths usually begin to 

 appear in small numbers during the latter part of April. This 

 spring brood of adults may be expected to reach the peak of emer- 

 gence around May 15 in Virginia and the Carolinas. On account 

 of the large proportion of small larvae overwintering, emergence of 

 the spring brood is delayed and continues until early in July. At 

 this time the population of adult moths is usually at a very low point. 

 The extended emergence of the spring brood results in consider- 

 able overlapping in later emergence; however, well-defined peaks 

 usually occur late in July or early in August and again during the 

 latter part of September. During the season when moths are active 

 a generation may be completed in about 60 days in stored tobacco. 

 The seasonal occurrence of the stages of the tobacco moth in Virginia 

 and North Carolina is shown in figure 6. 



422451°— 42 2 



