THE SUGAR-CANE MOTH BORER. 29 



emerging at the same time. This overlapping continues until by 

 midsummer the broods can not be separated. 



The maximum number of generations may be computed by taking 

 the first eggs laid by each generation and assuming that they would 

 develop under optimum conditions, thus reaching the adult stage in 

 the shortest time possible at the prevailing temperature: 



The first eggs in the spring, laid by adults from the hibernating larvse, 

 would hatch by May 1 and the adults appear by June 10. 



Adults of the first generation would lay eggs June 11, and these would 

 produce adults on July 24, after 43 days. 



Adults of the second generation would lay eggs on July 25, and these 

 would produce adults on September 1, after 38 days. 



Adults of the third generation would lay eggs September 2, and these 

 would produce adults on October 8, after 36 days. 



Adults of the fourth generation would lay eggs on October 9, and these 

 would produce adults on November 18, after 40 days. 



Adults of the fifth generation would lay eggs on November 18, and the 

 larvse would hibernate and emerge in the spring. 



On the other hand, it is equally possible for two generations to 

 span the entire year, if we take the last to emerge from hibernation 

 and allow them the maximum time for completing their life cycle. 

 The latest record of emergence is June 21, 1914, and a moth emerging 

 then would not oviposit before June 22 or 23. Eggs laid in the 

 insectary June 25, 1914, required 90 days to complete their cycle, the 

 adults not emerging until September 23. Larvse hatching the latter 

 part of August or in September frequently hibernate, so it is evi- 

 dent that the whole year could easily be taken up by two generations. 



These data are based on rearing notes in the insectary and on 

 observations in the field. While first-instar larvse have been found 

 in the fields from May 5 to the middle of December, and adults 

 have emerged in the insectary in December, it is seldom, if ever, that 

 the maximum number of generations are produced in the field. Most 

 of the larvse reared in the insectary have required from one and a 

 half to two or more times the minimum length of time necessary 

 to complete their life cycle, and there are usually only four, sel- 

 dom five, generations. If the spring is early and other conditions 

 favorable, there may be five generations, but if the spring is late 

 and cold, as it was in 1915, there will be only four. In the Rio 

 Grande Valley there is no true hibernation, although the stages are 

 prolonged somewhat in winter, and in Cuba they are more nearly 

 the same all the year around. 



POSSIBLE ANNUAL PROGENY OE ONE PAIR. 



It is on account of its rapid rate of reproduction that the borer 

 is able to inflict enormous damage. As almost all the larvse are 

 killed in the fall by grinding the cane, and as there is a high mor- 



