22 BULLETIN 746, U. S. DEPARTMENT OP AGRICULTURE. 



at once. They are active and can move about and lower themselves 

 with silken threads, but they do not seem to travel far from the place 

 of hatching. They go well down into the " bud " or whorl of the 

 plants, where they are protected from bright light and from possible 

 enemies, and they suffer no harm if, as is frequently the case, the 

 bud is full of water. Young larva? have often been observed to crawl 

 down into a bud which was completely submerged and feed for 

 several hours under water without any apparent discomfort. Some 

 of them at first eat only the epidermis from one side of the leaf, caus- 

 ing a yellowish blotch, but a little later they burrow through the 

 leaves while these are still unrolled. As one leaf is thus pierced in 

 a number of places at once a row of holes arranged horizontally will 

 be seen when it expands. Very often the larvae burrow into the 

 midrib, following a zigzag course for several inches along its length. 

 They can be seen very plainly by holding the infested leaves up to 

 the light. The larvae usually leave the buds or the midribs after the 

 first molt and crawl down between the leaf sheaths and the stalk, 

 some of them entering the stalk immediately and others feeding for 

 a day or two, or until after the second molt. It seems that the 

 larvae feed longer outside the stalks on old cane than on young plants. 

 The species of Diatraea which occurs at Phoenix, Ariz. (D. lineo- 

 lata) , has been observed to spend its entire larval and pupal periods 

 in the midrib. 



The larvae feed either up or down from the place of entrance, but 

 usually upward, producing a winding burrow or tunnel a foot or 

 more up the stalk. The burrows may be branched or two or more 

 may unite, forming a network of tunnels in a badly infested stalk. 

 The tunnels are quite small at first, but they are enlarged as the larvae 

 increase in size until they are one-eighth to one-fourth inch in diam- 

 eter, allowing the larvae to move about and turn round with freedom. 

 The frass is packed loosely behind the larvae, seldom completely clos- 

 ing the passages. The burrows usually become infested with the 

 red-rot fungus within a short time, causing the surrounding tissue to 

 turn red, the discoloration often extending for several inches beyond 

 the burrow (see frontispiece). 



CANNIBALISM. 



When larvae are confined in cages in the insectary they are canni- 

 balistic, especially in the smaller stages. If 200 or 300 newly hatched 

 larvae are left together they will be reduced to 40 or 50 within two 

 or three days. The smaller ones are usually eaten by the larger when 

 larvae of different stages are confined together, though full-grown 

 ones also are attacked. It seems that the larvae usually are attacked 

 when they are weak or inactive, especially just before or after molt- 



