15 



which have not will produce young after the leaves are removed, 

 as I have myself proved. 



Fields of unstripped cane that already contain leaf-hopper in 

 such numbers as to be doing considerable damage, are better left 

 in that condition, because a large proportion (in fact most) of the 

 eggs and pupae of some of the most active of its enemies are to 

 be found attached to the old dead or half-dry leaves, and some of 

 these enemies are more intolerant of exposure by stripping than 

 are the leaf-hoppers themselves. 



DIFFERENCE IN SEVERITY OF LEAF-IIOPPER ATTACK ON NEIGHUOR- 

 ING PLANTATIONS 



10. In some cases it is evident that neighboring plantations 

 have suiTered from the attack of leaf-hopper in a very diiferent 

 degree. This is due to several causes and sometimes obviously 

 (i) to the difference in the length of time that the leaf-hopper has 

 been present in large numbers. Thus a limited area in a district 

 becomes first badly infected and when this spot has produced a 

 superabundant supply of the pest, it spreads (sometimes in a 

 migratory swarm) over a much larger adjoining area, which suf- 

 fers greatly, while the cane immediately adjoining this larger area 

 is not much injured. (2) Slightly different climatic causes 

 probably exert a restraining influence or the reverse. (3) In 

 some cases the number of natural enemies of the leaf-hopper (es- 

 pecially the numbers present when first it has occupied a new 

 locality) may turn what threatens to be a bad outbreak into a 

 light attack. In some cases the fact that on adjoining plan- 

 tations the seriousness of the attack diifers greatly seems inexplic- 

 able, and due only to that apparent capriciousness of the insect, 

 of which I have already spoken. 



Some eight months ago I wrote in my report, "There is little 

 doubt that its destructiveness will vary very much with the lo- 

 cality and according to the season and it is by no means certain 

 that it has as yet, even on Oahu, multiplied to the fullest extent.'' 

 Later observations have fully convinced me of the truth of these 



