THE SUGAR-CANE MOTH BORER. 35 



SURVIVAL OF HIBERNATED LARVAE. 



Only a small proportion of the larvae which go into hibernation 

 survive the winter and emerge as adults. They die from time to 

 time during the winter and those which have been in the larva stage 

 for a long time seem to have trouble in pupating and often die in 

 the attempt. Then, too, the mortality is higher among the pupae 

 from hibernated larvae than from others, and the adults that emerge 

 are not so vigorous. 



Not more than 10 per cent of the larvae kept under insectary condi- 

 tions emerged, and as those pupating in the field often have the addi- 

 tional trouble of emerging through some depth of soil, it is evident 

 that only a small percentage survives. On account of their rapid 

 increase in numbers it requires only a few moths in the spring to 

 produce a large number of borers during the summer and fall. 



LONGEVITY OF HIBERNATED LARVAE. 



The usual larval period is greatly prolonged by cold weather or 

 other adverse conditions, and the larvae can survive great hardships. 

 It is not at all uncommon for them to live for a month or two with- 

 out food, and Stubbs and Morgan (152) have kept them for 75 

 days without food and had them pupate afterwards. Kosenfeld and 

 Barber (137) kept a larva for 200 days without food and it pupated, 

 while E. R. Barber records placing a larva in the photographic 

 dark room on October 19, and finding it alive June 9, a period of 231 

 days, during which it did not feed on the piece of sugar cane pro- 

 vided. The larva stage of overwintering individuals is generally 

 about 7 or 8 months, and during this time there are 10 or 12 molts, 

 but in the authors' experiments some required 276 days and 14 molts 

 to reach the pupa stage. 



NATURAL CONTROL. 

 CLIMATIC CONTROL. 



EFFECT OF RAINFALL. 



Mr. George N 7 . Wolcott, while entomologist of the Insular Experi- 

 ment Station, Rio Piedras, Porto Eico, made a number of observa- 

 tions which tend to prove that the moth borer is adversely affected 

 by rainfall. The following is an abstract of Mr. Wolcott's conclu- 

 sions : 



A large number of careful observations made in Porto Rico during the past 

 grinding season, confirmed by the evidence from other countries, indicates that 

 there is a constant relation between the amount of rainfall and the abundance 

 of Diatraea. The table, which gives the percentage of infestation of cane 

 by Diatraea in conjunction with the total annual rainfall in inches for 1914, 



