20 



CIRCULAR 4 2 2, U. S. DEPARTMENT OF AGRICULTURE 



In order to show graphically the seasonal occurrence of the tobacco 

 moth in 1932 and 1933 the data are presented in figure 8. The spring 

 brood of moths, which is composed of a small percentage of the first- 

 generation larvae, approximately 50 percent of the second, and all of 

 the third of the preceding year began pupating approximately March 

 15, and emergence began approximately April 10. These dates are 

 based upon laboratory life-history studies and many observations 

 made in tobacco factories and warehouses during the period 1932 to 

 1934 in Virginia and North Carolina. 



CONTROL 



NATURAL ENEMIES 



The tobacco moth has an important enemy in the small braconid 

 parasite Microbracon hebetor (Say) (fig. 11). The sting of this 

 small wasplike insect in a well-grown larva of the moth results in 



complete paralysis 

 of the larva in a few 

 minutes. Eggs are 

 then deposited be- 

 neath or attached to 

 the body of the host 

 larva. These eggs 

 hatch in about 2 

 days, when the tem- 

 perature is above 70° 

 F., and the young 

 parasite grubs feed 

 voraciously on the 

 body of the moth 

 larva. A total of 

 1,900 egg -to -adult 

 rearings of the para- 

 site were made in the 

 laboratory, grown 

 larvae of the tobac- 

 co moth being used 

 as hosts, and records of egg deposition and longevity were com- 

 pleted for 14 females. A summary of these records shows the fol- 

 lowing averages : Incubation period 2 days, larval period 3.4 days, 

 pupal period 5.2 days, egg-to-adult period 14.5 days. The highest 

 number of eggs obtained from one female parasite was 517 and the 

 lowest was 96. The average of the 14 females was 323 eggs each. 

 The temperatures ranged from 65° to 85° during the time the fore- 

 going records were being obtained. The shortest egg-to-adult period 

 recorded for the tobacco moth was 39 days (table 6) . It is estimated 

 that under favorable conditions from two and one-half to three gen- 

 erations of this Microbracon* will develop for each generation of the 

 tobacco moth, and that on the average the parasite will reproduce at 

 approximately three times the rate of the moth. These factors would 

 appear to give the parasite a tremendous advantage in tobacco stor- 



Figure 11. — The parasite Microbracon hebetor in the act of 

 stinging a larva of the Mediterranean flour moth, 

 Ephestia kuehniella. X 10. 



