36 BULLETIN 746, U. S. DEPARTMENT OE AGRICULTURE. 
shows that the abundance of Diatraea is in inverse proportion to the amount 
of rainfall. (The table mentioned shows that the infestation varies from 6 per 
cent, where there were 101 inches of rain, to 66 per cent, where there were 
only 21 inches.) . . . 
It is comparatively easy to demonstrate the effect of an abundance of rain- 
fall in lessening the numbers of Diatraea, but much more difficult satisfactorily 
to account for this effect. The eggs of the borer are deposited on the leaves 
of the cane, and when the young larvae hatch, a considerable interval elapses 
while they crawl about on the cane before they enter the stalk or the midrib 
of the leaf. It is quite probable that this is one of the most crucial periods 
in its life history, and that considerable numbers of borer larvae were killed 
in young cane by the more rapid growth of the central shoot of a cane plant 
than of the outer leaves. Also, larvae were found which had been drowned in 
a mixture of water and decaying cane juices which had collected in their tunnels 
after rains. To avoid danger from these causes, many larvae were found living 
outside the shoot, where they were exposed to the attacks of predators or 
parasites. 
The rainfall over the sugar belt of Louisiana does not vary to any 
great extent, and while there are annual differences both in infesta- 
tion and rainfall at various points, a careful study of the subject has 
failed to prove that these variations correspond as they do in Porto 
Rico. 
Below is given the infestation by the moth borer at various places 
in 1916 as compared with the annual rainfall. 
Infestation by the moth borer compared with annual rainfall at various places 
in Louisiana. 
Canes 
Annual infested 
rainfall. in fall. 
Place. Inches. Per cent. 
Donaldsonville T 61. 51 91 
White Castle 50 to 60 99 
Thibodeaux 50 to 60 79 
Mathews 50 to 60 97 
Palmetto 50 to 60 37 * 
Franklin 58. 89 53. 5 
New Orleans : 55. 37 38 
Kapoleonville 54. 96 95 
Lafayette 54. 68 99 
Melville 51. 98 22 
Abbeville 50. 39 9S 
Morgan City - 47. 69 93. 5 
The period during which the growing cane is attacked by the borer 
in Louisiana is, roughly, from the month of April to the month of 
October, inclusive. A graphic comparison of the rainfalls during 
these months for the years 1912, 1913, 1914, 1915, and 1916 with the 
average infestations by the borer in the fall of each year is shown 
in figure 10. In some years the line representing infestation descends 
as the line representing rainfall ascends, but there were exceptions, 
especially in 1916, which the authors can not explain. Mr. Wolcott 
suggests that the small variation in the rainfall at different points 
1 Probably flooded. 
