11 



MIGRATORY SWARMS OF THE LEAF-HOPPER. 



5. As has been already stated, the leaf-hopper of the cane is 

 nocturnal in its habits, and these insects are not seen on the wing 

 by day except casually or when disturbed. On certain occasions, 

 however, they have been seen flying in one direction in the day 

 time m such numbers as to form a migratory swarm, fjuite like 

 that which occurs in the case of certain locusts, dragon-flies, but- 

 terflies and other insects. 1 am not aware that such migrations 

 have been recorded previou,sly of leaf-hoppers, but they are known 

 to be undertaken by the somwhat allied group of Aphidac. It 

 would appear from observations made, that these leaf-hopper 

 migrations are largely due to the fact that the food supply in the 

 place whence they originate has become exhausted or impover- 

 ished by the number of the insects. 



SIGNS OF LEAF-IIOPPER ATTACK AND ITS RESL LTS. 



6. \\'hen leaf-hoppers are present in large numbers the mid- 

 rib and sheath of the leaf often become conspicuously red either 

 in spots or almost wholly, but such an appearance may be due to 

 other causes. The minute discolored scars marking the opening 

 of the egg chambers are a certain sign of the presence of the in- 

 sects, even though thc}^ may not themselves be noticed. I de- 

 tected the presence of the pest by these scars (on samples of cane 

 sent for examination for other reasons) on certain plantations 

 where at the time the leaf-hopper was said not to exist at all. Like 

 other insects of their sub-order, leaf-hoppers excrete large quanti- 

 ties of a clear, sweet liquid, called honeydew, and on this the 

 usual fungi grow. Consequently in bad attacks whole fields of 

 cane may be black with the usual black fungus, or in striking 

 contrast, white with another species, or the black smut may be 

 followed and overgrown with the white fungus. Either of these 

 fungi, however, may follow bad attacks of other insects that 

 excrete honeydew, while on the contrary, bad attacks of leaf-hop- 



