October, '15] 



WOLCOTT: DIATR.EA SACCHARALIS 



497 



organisms to enter, reducing the amount and purity of the juice, and 

 weakening the strength of the stalk. The pupa is formed in the stalk, 

 and the creamy-yellow, inconspicuously marked moths deposit eggs 

 on the upper leaves of the cane. 



The writer has visited most of the cane growing countries, and, 

 being impressed by the notable variation in the amount of cane in- 

 fested with the borer larvse, has endeavored to determine the fac- 

 tors governing the abundance of the insect. 



Working along similar lines in Louisiana, Mr. T. E. Holloway has 

 contended {Louisiana Planter, December 19, 1914) that the abun- 

 dance of Diatrcea depends in large part upon the scarcity of the cos- 

 mopolitan and omnipresent egg parasite of the borer, Trichogramma 

 minutum. Field experiments in Texas and Louisiana, carried on for 

 two years by ]\lr. Holloway, have quite effectually demonstrated that 

 the burning of the cane trash (tops and leaves) after the cane is har- 

 vested, destro3's large numbers of Trichogramma, as is evidenced by a 

 larger number of cane stalks injured by Diatrcea in the succeeding crop 

 than in check fields where the trash is not burned. 



A large number of careful observations made in Porto Rico during 

 the past grinding season, confirmed by the evidence from other coun- 

 tries, indicates that there is a constant relation between the amount 

 of rainfall and the abundance of Diatrcea. The accompanying table, 

 which gives the percentages of infestation of cane by Diatrcea in con- 

 junction with the total annual rainfall in inches for 1914, shows that 

 the abundance of Diatrcea is in inverse proportion to the amount of 

 rainfall. In the table, the abundance of Diatrcea in fields where the 

 trash was burned, and where the trash was not burned, is recorded 

 separately, the difference amounting to nearly 100 per cent higher 

 infestation by borer in fields where the trash has been burned. 



That rainfall affects the abundance of the smaller moth borer 

 is of scientific interest, but apparently no economic application can be 

 made of this fact. But it is possible for planters to take advantage of 

 the relation which has been found to exist between trash burning and 

 borer infestation, and stop burning trash. In Cuba and northern 

 Porto Rico, trash is seldom burned, and practically never in the 

 British colonies. With a better understanding of the losses attendant 

 upon burning the trash, it can usually be obviated elsewhere by the 

 use of improved heavy-ratooning varieties and somewhat altered 

 plantation practice. 



It is comparatively easy to demonstrate the effect of an abundance 

 of rainfall in lessening the numbers of Diatrcea, but much more difficult 

 to satisfactorily account for this effect. The eggs of the borer are 

 deposited on the leaves of the cane, and when the young larvse hatch, 

 a considerable interval elapses while they crawl about on the cane 



