HAWAIIAN ISLANDS 375 



36-2 per cent, to 56-4 per cent, of the fruit-fly larvae are parasitised. 

 It is recognised that, although a sufficiently high degree of control 

 from the commercial standpoint has not been obtained, the 

 parasites have decreased the infestation to a marked extent. 

 While coffee cherries and guavas have been largely freed from 

 infestation, other fruits, like the mango, which have a thick pulp, 

 are much more severely attacked, since the parasites are unable 

 to reach many of the Ceratitis larvae within them. With the 

 object of effecting a more adequate measure of biological control 

 of this insect, entomologists are now engaged in studying the 

 possibility of further parasite introductions to this end being 

 effected from abroad. 



It would require too much space here to recount all the 

 examples of biological control attempted or achieved in these 

 islands : a chronological list of them up to about 1930 is given in 

 the book by Williams (1931). At the present time the horn-fly 

 pest of cattle is still uncontrolled, and the same applies to the 

 pineapple mealybug, and some other pests. It must not be 

 assumed that success in biological control in these Islands has 

 come easily, or that every beneficial insect introduced has become 

 established in its new surroundings. A history of the subject 

 would have to record a number of failures, and the expenditures 

 of strenuous effort and large sums of money. Thus, the complete 

 control of the cane leaf hopper only resulted after the introduction 

 of about a score of different parasites and after about twenty 

 years of work. On the other hand, the control of the Anomala 

 beetle and the avocardo mealybug was achieved in a remarkably 

 short interval of time. 



Viewed as a whole, biological control has achieved a degree of success 

 in the Hawaiian Islands not so far attained elsewhere. The majority of 

 the important pests have become subjugated by this method, and there 

 is little necessity for the application of insecticides. At the same time 

 it must be remembered that the limited area of the terrain, its isolation, 

 and its warm, equable climate, all favour measures of this character. 

 Beneficial insects can be introduced at almost any time of the year, and 

 are able to pass through uninterrupted cycles of development owing 

 to the absence of a dormant season. It is true that such conditions 

 conduce to the multiplication of pests, but they are at least as 

 favourable to parasites and predators. Furthermore, the unique 



