THE SUGAR-CANE MOTH BORER. 



25 



period the larvae attain a length of from 6 to 9 mm. The third 

 instar is somewhat longer and requires from 6 to 9 days, the larvae 

 reaching 10 to 15 mm. in length, while the fourth instar lasts from 

 4 to 6 days, at the end of which the larvae are 15 to 20 mm. long. 

 From 3 to 6 days are spent in the fifth instar, and the larvae attain a 

 length of from 20 to 30 mm. 



The usual time required for the larva stage under favorable con- 

 ditions is from 25 to 30 days in summer and from 30 to 35 days in 

 the cooler weather, but it may be much longer. Larvae from the same 

 mass of eggs and reared under exactly the same conditions vary a 

 great deal, and some of them require two or three times as long as 

 others to pupate. Under the most favorable conditions the larval 

 period has been as short as 18 days, and has varied from this to 276 

 days for hibernating larvae. The larvae are very adaptable in this 



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Fig. 8. — Diagram showing relationship of mean temperature to length of larval period 

 of the sugar-cane moth borer. The dots represent period means of individuals. 



way and can pass over periods of cold or food shortage without 

 serious inconvenience. Typical life histories at different seasons of 

 the year are shown in Table V and figure 8. 



Table V. — Relationship of mean temperature to developmental period in larva 

 stage of the sugar-cane moth borer. 



Mean tem- 



Average 



Number 



Mean tem- 



Average 



Number 



perature. 



period. 



of records. 



perature. 



period. 



of records. 



°F. 



Days. 





°F. 



Days. 





59.4 



246.5 



2 



78.7 



25 



1 



59.6 



216 



2 



79.1 



42 



4 



59.8 



232.5 



5 



79.5 



24 





60 



221 





79.6 



29 





60.3 



225 





79.7 



26 





60.4 



224 





79.8 



23.5 





60.5 



233 





79.9 



23 





60.7 



248 





80 



28 





60.9 



262 





80.1 



33 





61.4 



242 





80.3 



48.5 





65.3 



63 





80.4 



31 





65.6 



76 





80.5 



57 





65.7 



74 





80.6 



38 





67.6 



65 





80.7 



49 





68.7 



56 





80.8 



42 





68.8 



52 





80.9 



46 





