12 FAEMERS BULLETIN 846. 



of Virginia and Tennessee there are three or four generations a year. 

 The time required to complete the life cycle of the insect depends 

 mainly upon temperatuje and may be as short as 45 days, normally 

 varying in summer from 45 to 70 days. Eggs are laid in the food 

 substance. They hatch in from 6 to 10 days. The larva period is 

 from 30 to 50 days and the pupa period from 6 to 10 days. T^^nder 

 usual conditions adults live from three to six weeks. In temperate 

 climates the insect passes the winter mainly in the larva stage. It 

 thrives best Avhere the temperature and humidity are high and in 

 tobacco or other food substances protected from rapid evaporation. 



SEASONAL ABUNDANCE AND NUMBER OF GENERATIONS. 



In food substances kept constantly warm all stages of the beetle may 

 be found at any time, and the great variation in the time required for 

 development gives constant overlapping of generations. Under usual 

 conditions in tobacco Avarehouses and in unheated buildings there are, 

 however, well-marked periods when the adults are most abundant. 

 In the latitude of Virginia and Tennessee there seems to be a period 

 of greater abundance of the adults coinciding with the first warm 

 weather in June, and again in August and early September. At 

 Clarksville, Tenn., starting with the egg stage, in early May, three 

 or, under some conditions, four generations are possible. At Rich- 

 mond, Va., three generations may occur under warehouse conditions 

 before the appearance of cold weather, the adults appearing in May, 

 July, and October, and from the adults emerging earliest in the 

 spring there may possibW be a fourth generation reaching the adult 

 stage before winter. 



NATURAL CHECKS. 



Several natural agencies serve to check the increase and spread 

 of the tobacco beetle, among which are low temperature, the drjdng 

 out of food, the molding of food, parasitic and predator}' insects, 

 mites, jointed spiders, and false scorpions. 



CLIMATIC CONTROL. 



In the temperate zone a comparatively small proportion of the 

 insects survive the winter when exposed to even moderate cold, long 

 continued, or to sudden abnormal changes in temperature. Severe 

 freezing at temperatures lower than 10 degrees above zero (Fahren 

 heit), even for a short time, exterminates them completely. Evi- 

 dences of the effect of freezing: on the tobacco beetle have been ob 



