222 SCIENCE PROGRESS 



adopted for keeping this pest under control, it may be men- 

 tioned that by this means, " under proper management, a forest 

 can be protected at a moderate expenditure, or almost without 

 cost where there is a market for the timber." 



Leaving the work of the Central Bureau, attention may be 

 directed for a few moments to the energy and resourcefulness 

 with which investigations in economic entomology have been 

 conducted during the last few years by Americans in Hawaii — 

 the working centre having, as already mentioned, assumed the 

 form of an experimental station founded, and apparently sup- 

 ported, by the Sugar-Planters' Association in Honolulu. For 

 many years past sugar-growing in the Sandwich Islands has 

 been heavily handicapped owing to injuries inflicted on the 

 canes by an insect commonly known as the sugar-cane leaf- 

 hopper, and technically designated Perkinsiella saccharicida. 

 The leaf-hoppers, it may be mentioned, belong to the order 

 Hemiptera or Rhynchota, which includes some of the most 

 mischievous insects in the world. 



The harmfulness of the Hemiptera, or " plant-bugs," is 

 indeed very largely due to the excessive rapidity of the increase 

 of these insects — an increase so great as to suggest that, were 

 it not for the restraining effects of parasites, these insects would 

 in the course of a few years destroy all the vegetation on the 

 face of the earth. 



As regards the leaf-hoppers themselves, they are preyed 

 upon by a large number of insects belonging to numerous 

 orders and families ; and at an early stage in the inquiry as 

 to the best means of restraining the ravages of the Hawaiian 

 species, it was recognised that the most promising results were 

 likely to accrue from the introduction and cultivation of one or 

 more parasitic species. Accordingly, arrangements were made 

 for dispatching scientific missions to various parts of the world 

 with the object of obtaining as much observation as possible 

 with respect to such parasitic species. Of these expeditions the 

 Bulletin published at Honolulu (referred to in the list of litera- 

 ture at the close of this article) is the outcome. A better and 

 more exhaustive piece of work has, perhaps, seldom been 

 accomplished, forming as it does a most elaborate account of 

 the various groups of parasites known to infest the leaf-hoppers, 

 together with a resume of the life-history of the hoppers them- 

 selves. Furthermore, the notes in regard to the best means of 



