28 



BULLETIN 746, U. S. DEPARTMENT OF AGRICULTURE. 



secured. The sum of the periods required by most individuals in the 

 various stages is 43.1 days, which may be regarded as an average. 

 The maximum larval period. is 262 days and only occurs in hiber- 

 nating larvae. 



SEASONAL HISTORY. 



SEASONAL ABUNDANCE. 



NUMBER OF BROODS OR GENERATIONS. 



The variation in the time required for the development of the moth 

 borer is so great that there are no distinct broods or generations. It 

 is found that some larvaB require three or four times as long to reach 

 the adult stage as others hatching from eggs laid at the same time, 



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Fig. 9. — Diagram showing relationship of mean temperature to length of pupal period 

 of the sugar-cane moth borer, showing line of calculated means (dashes) and general 

 trend of means (solid line). The dots represent period means of individuals. 



and this causes such an overlapping that the broods can not be 

 distinguished. 



The time of emergence of the moths in the spring varies from year 

 to year, depending on the season. The earliest record is of a first- 

 instar larva collected on cane in the field on May 5, 1914, and as the 

 eggs require from G to 7 days incubation at this season the moth 

 must have emerged during the last few days of April. The first 

 emergence in the insectary was not until May 8, and emergence con- 

 tinued until May 25. Adults emerged from cane planted in boxes of 

 soil as late as June 21. A pupa from the spring brood of borers was 

 found in a " dead heart " on June 2, 1914. Thus adults from the 

 hibernating larvaB and adults from the first spring generation are 



