THE PESTS AND DISEASES OF THE CANE 147 



Guiana, for example, the " moth borer," though severely parasitized, an- 

 nuall} 7 causes great damage, and up to the present no parasite has been re- 

 corded as controlling the " large moth borer" there present and an indigenous 

 species. Similarly, the island of Trinidad, which from its proximity to the 

 mainland is rather of the continental than the insular type, has suffered 

 very severely from an epidemic of the cercopid " frog hopper," Tomaspis 

 posticata. 



The second condition obtains in islands remote from the mainland 

 which generally possess a very restricted fauna. As instances of such dis- 

 tricts may be cited the Hawaiian Archipelago and the islands of Mauritius 

 and Bourbon. The more remote West Indian islands would also fall into 

 this category, while the islands of Cuba and Java, from their proximity 

 to the mainland, would be more of the continental type. Under the second 

 condition the introduction of predatory insects is likely to cause a severe 

 epidemic and several such have been quoted in a previous section. These 

 epidemics may be regarded as caused by the disturbance of the " natural 

 balance." 



When a crop becomes subjected to insect damage, periods of greater 

 and of less incidence are observed. This observation also follows a natural 

 cycle. At one period the pest may be present in great numbers. The 

 parasite, if present, then has unrestricted opportunity to carry out its life 

 work, and the epidemic period is followed by the partial disappearance 

 of the pest. The parasite now has less material on which to work so that 

 its numbers tend to decrease, and consequently the pest again appears in 

 quantity. The incidence of the pest will also be controlled by seasonal 

 variation, some seasons being favourable to the development of the pest 

 and some to that of the parasite. The matter is further complicated by the 

 presence of hyper parasites, which have the same relation to the parasite 

 that the parasite has to its host. As instances of parasitization and of 

 hyperparasitization, the observations of Ulrich 45 in Mexico may be quoted. 

 He there found that the frog hopper, Tomaspis posticata, was attacked by a 

 reduviid bug, Castolus plagiaticollis, the eggs of the bug being parasitized 

 by a hymenopteron, Telenomus sp. Similarly in Fiji the efficiency of the 

 introduced tachinid parasite of the beetle borer was found by Illingworth 46 

 to be depreciated by the presence of an ant, Pheidole megacephala, which 

 acted as a predator on the fly. 



Occasionally instances are observed where a factor is inimical to both host 

 and parasite ; such a combination is recorded by Ritchie, 47 who, in the West 

 Indies, observed ants preying both on the " cane fly," Delphax saccharivora, 

 and on its syrphid parasite. 



In addition to the parasitization of insect by insect, various fungi have 

 been observed to attack and thus to control insects. The effectiveness 

 of this control does not yet seem to have been worked out. Speare 48 has 

 made a study of parasitic fungi affecting various pests, and has recorded the 

 presence of Entomophthora pscudococci and Aspergillus parasiticus on the 

 mealy bug, Pseudococcus sp. ; of the green muscardine fungus, Metarrhizium 

 anisoplice on the Hawaiian beetle borer ; and of Cordyceps sp. on the leaf 

 hopper. The green muscardine fungus appears to be of very wide distribution, 

 and it has been specially studied by Rorer 49 in connection with the frog 

 hopper in Trinidad, where it has been artificially grown on the large scale 

 and distributed over infected areas. Similarly Cordyceps is also widely 

 distributed, and it has been recorded on the caterpillar of the West Indian 



