30 BULLETIN 740, U. S. DEPARTMENT OF AGRICULTURE. 



tality among those which escape and hibernate, it is evident that 

 comparatively few emerge in the spring. Yet there is always a 

 heavy infestation by fall. The rapidity of reproduction during the 

 warm months is the only factor which can account for this high 

 infestation. 



The record of oviposition for 56 moths at various times during 

 the season of activity shows that each female moth deposits on an 

 average 210 eggs. The sexes are produced in equal proportions. 

 Allowing 200 eggs for each female and four generations a year as a 

 conservative estimate, it is found that each pair surviving the winter 

 is capable of producing the following numbers : 



Generation. Borers. 



First 200 



Second 20, 000 



Third 2, 000, 000 



Fourth 200, 000, 000 



Total 202,020,200 



Of course this maximum number will never be produced, because 

 of the numerous checks which control the insect, but something of 

 its enormity may be realized by considering that if the offspring 

 of one female were confined to 1 acre there would be over 10,000 

 borers per stalk of cane, about 20,000 stalks being the average per 

 acre. Under average conditions about 50 per cent of the stalks are 

 infested and about 25 to 30 per cent of the infested stalks contain 

 borers when cut for the mill, giving from 2,500 to 3,000 borers per 

 acre. Considering the possibilities, it is only surprising that the 

 infestation is not much higher. 



PROGRESS OF INFESTATION. 



The moth borer is late in developing in the spring. The first 

 " dead heart " at New Orleans is usually found about the 1st of May, 

 which indicates that moths have emerged from hibernation several 

 weeks previously. Not much injury can be found through the sum- 

 mer, but the numbers of borers gradually increase. When the corn- 

 stalks become dry in July and August the emerging moths un- 

 doubtedly migrate to sugar-cane fields in large numbers. The 

 infestation increases rapidly from about this time until the cane is 

 cut for grinding. 



STATUS EXAMINATIONS. 



Field examinations to determine the annual status of the moth 

 borer and other sugar-cane insects have received considerable atten- 

 tion from the writers. The best and practically the only time to 

 determine borer injury to sugar cane is during the grinding season 



