BIOLOGY OF TOBACCO MOTH AND ITS CONTROL 21 



ages, but the writers have been unable thus far to devise a satisfactory 

 system of measuring the factors which apparently reduce the effec- 

 tiveness of the parasite. 



Observations in tobacco warehouses showed that these parasites 

 overwinter as adults and pupae at or near the surface of hogsheads 

 or bales of tobacco, and in cracks of walls or ceilings. These loca- 

 tions exposed the insect to the lowest temperatures in winter, and 

 this was believed to be a factor of importance in reducing the popu- 

 lation. In some warehouses infested by the tobacco moth no para- 

 sites were observed during the development of the first-generation 

 larvae, but by September 15 they had increased to a point where 

 thousands were seen on the surfaces of the tobacco and on windows 

 of the warehouse. The individuals crawling on the closed windows 

 were probably attempting to escape because of a shortage of host 

 larvae. Experiments with light traps show the adult parasites to be 

 positively phototropic but only to a small degree. 



The other natural enemies of the tobacco moth observed in ware- 

 houses were mites of the genus Laelaps, which attach themselves to 

 adults, and a spider, Theridion tepidariovum Koch, which sometimes 

 constructs considerable webbing in which hundreds of moths are 

 captured and destroyed. Neither the mites nor the spiders, however, 

 have been observed to be of material aid in controlling moth 

 infestations. 



TEMPERATURE 



The conclusion was reached, based on many observations in ware- 

 houses, that overwintering larvae of the tobacco moth can withstand 

 the low temperatures occurring in winter in Virginia and the Caro- 

 linas without heavy mortality. Therefore low temperatures in stor- 

 age warehouses cannot be considered as a natural control of hibernat- 

 ing moth larvae. 



ARTIFICIAL CONTROL IN CLOSED STORAGE 



INSECT TRAPS 



Traps in which a combination of suction and light is used were 

 tested in tobacco warehouses against the adults of the tobacco moth. 

 These traps have proved ineffective, as shown by experiments of 

 Reed et al. (19, p. 12), and cannot be recommended for use in ware- 

 houses against the insect. 



PERIODIC ATMOSPHERIC FUMIGATION 



From 1930 to 1932 the writers carried out fumigation experiments 

 at atmospheric pressure in tobacco warehouses for the control of 

 the tobacco moth. Hydrocyanic acid was used in the experiments, 

 at dosages ranging from 4 to 24 ounces per 1,000 cubic feet, with 

 exposures ranging from 12 to 72 hours. During the early stages of 

 the work in 1930, it became apparent that if satisfactory results were 

 to be obtained from the fumigation of warehouses, care must be 

 exercised in sealing the infested buildings (7, p. 6). and in many 

 instances fumigations must be repeated at intervals. 



