EFFECT OF VARIOUS NATURAL ENEMIES IN CON- 

 TROLLING LEAF-HOPPER. 



Flaving dealt with the introduction, propagation and distribu- 

 tion of the several parasites, we will now consider the practical 

 efifect of these and other natural enemies in diminishing the leaf- 

 hopper pest. There are yet in AustraHa and Fiji, as can be 

 seen by the student of the various Parts of this Bulletin, a num- 

 ber of other natural enemies of leaf-hoppers, which, introduced, 

 would certainly attack our cane leaf-hopper, though either we 

 did not attempt to introduce these, or were unsuccessful in the 

 attempt. I have already, in my last annual Report to the Com- 

 mittee on the Experiment Station, stated what parasites we 

 especially desired to import and the reasons for this, but for the 

 sake of completeness, I here make some repetition. Thus in 

 choosing what natural enemies it was desired to introduce, we 

 had to consider: (i) their effectiveness or importance as de- 

 stroyers of the pests ; (2) the possibility of successful transporta- 

 tion ; (3) the probability of their thriving in a new country ; (4) 

 the rapidity of their increase, when established. On the firf.t 

 two heads, there is nothing special to remark, but the third was 

 a matter of great importance. When one considers the excessive 

 difference in climate between many of the plantations, the ex- 

 tremes being shown by one where cane is grown on the wind- 

 ward side at an elevation of about 1 500 or more feet, with its ex- 

 cessive rainfall, and one nearly at sea level on the dry leeward 

 side, where cane can exist only by constant irrigation, it is ob- 

 vious that comparatively few species of insects can be expected 

 to thrive equally well under such diverse conditions. Conse- 

 quently we had need primarily of parasites of wide-spread range 

 in their own country, not such as were of local occurrence only. 



The fourth consideration, that is the rate of increase, was to 

 us of the greatest importance, since we had to deal with a pest 

 already established for years, and that had no doubt reached its 

 average numerical maximum throughout the islands. In this 

 the little Mymarid egg-parasites of the genera Aiiagnts and 

 Paranagnis excel. They complete their life cycle in about three 

 weeks in these islands, and apparently breed at the same rate, or 

 nearly so, at all seasons of the year. Further they are largely 

 parthenogenetic. the male sex being only produced at rare in- 

 tervals. 



