July i 7> 1916 Larval Characters and Distribution of Diatraea spp. 6-23 



difficult to determine the exact extent of the tubercles. The writer 

 found that the positions of setae i and ii correspond with the tubercles 

 of the same numbers and that imaginary lines through the bases of the 

 two setae on each side form different angles in the two species. By the 

 use of a camera lucida the relative positions of the bases of setae i and ii 

 on segments 3, 4, and 5 of 19 specimens of D. saccharalis crambidoides 

 and of seven specimens of D. zeacolella were determined, lines were drawn 

 through the points representing the bases of the setae, and the resulting 

 angles were measured. It was found that the average angle for D. sac- 

 charalis was 30.2 , while for D. zeacolella it was 53. 3 . The size of these 

 angles and the position of the lines through the bases of the setae are 

 graphically indicated in figure 1. 



In different specimens the angles were found to vary from 41 ° to 69. 5 

 in D. zeacolella, and from 18 to 41. 5 ° in D. saccharalis crambidoides. 

 Angles of the minimum and maximum numbers of degrees are exceptional. 



The differences in the larval characters are noted in the following 

 comparison : 



' Diatraea saccharalis crambidoides Fabricius. 



Tubercles light brown or paler (summer 

 form) . 



Head brown, but may occasionally be 

 yellow in winter form. 



Spiracles dark brown. 



Abdominal tubercles i hardly twice as 

 large as abdominal tubercles ii, more 

 nearly equal. 



Abdominal tubercles ii oval, and about 

 twice as far apart as abdominal tuber- 

 cles i. 



Two imaginary lines connecting bases of 

 setae i and ii of abdominal segments 3, 

 4, and 5, on each side, if prolonged, 

 form angles averaging 30.2 . 



Diatraea zeacolella Dyar. 



Tubercles dark brown, contrasting 

 sharply with ground color of body 

 (summer form). 



Head yellow. 



Spiracles black. 



Abdominal tubercles i about twice as 

 large as abdominal tubercles ii. 



Abdominal tubercles ii narrowed and 

 about four times as far apart as abdom- 

 inal tubercles i. 



Two imaginary lines connecting bases of 

 setae i and ii of abdominal segments 3, 

 4, and 5, on each side, if prolonged, 

 form angles averaging 53.3 °. 



Descriptions of full-fed larvae of both the summer and the winter ii rms 

 of the two species are given below. 



Diatraea saccharalis crambidoides Fabricius. 



Summer form. — Head rich brown, varying to black at mouth parts and to orange 

 on dorsal aspect; slightly bilobed. Prothoracic plate pale brown, tinged with black 

 ventrally, cephalic third of plate transparent. Body white. Segmentation dis- 

 tinct. Crochets biordinal. Tubercles light brown or paler, iv and v coalesced. 

 Abdominal tubercles ii oval and about twice as far apart as tubercles i. Primary 

 setae yellow to brown. Imaginary lines connecting setae i and ii of abdominal seg- 

 ments 3, 4, and 5, on each side, if prolonged, form angles averaging 30. 2° . No second- 

 ary setse. Spiracles dark brown, elongate oval, distinct. Average length (10 Speci- 

 mens), 25.6 mm. 



