THE SUGAR-CANE MOTH BORER. 



23 



ing. Three or four larvse often are found living in the same stalk 

 of cane, but in these cases they are more or less separated by their 

 burrows, and it is not likely that large larvse are eaten by others 

 under field conditions, where they have freedom of action, whereas 

 the habit of small larvse of congregating in the terminal buds of the 

 plants is very conducive to cannibalism, and many doubtless are 

 destroyed by their companions. 



GROWTH. 



The rate of growth is dependent upon many external conditions, 

 the temperature and kind of food being the most important factors, 



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Fig. 7. — Diagram showing relationship of mean temperature to larval growth of the 

 sugar-cane moth borer per day in hundredths of millimeters, showing line of maxi- 

 mum growth of normal individuals. The dots represent growth of individuals in 

 hundredths of millimeters. 



but larvse feeding under similar conditions show a great variation 

 in the rate of development and in the length of the larval period, as 

 is shown by figure 7. Under favorable conditions the rate of in- 

 crease in body length is about 0.75 mm. per day, but it is often much 

 less. Larvse are from 1.5 to 2 mm. long when hatched and from 25 

 to 30 mm. long when fully grown. 

























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Before molting the larvse stop feeding for a few hours or some- 

 times longer and appear stiff and helpless. The skin then ruptures 



