ENTOMOGENOUS FUNGI ^j 



tage at the beginning of an attack, the former do not become 

 very effective until their hosts are plentiful. Like all fatal 

 parasites, they tend to cut their own throats. The more 

 thoroughly they kill off their hosts, the less material they have 

 to live upon. When the chances of infection have been thus 

 reduced, the surviving insects, or colonists from another area, 

 start a fresh wave of insect infestation, which in time is again 

 overtaken by the rising numbers of the parasite. 



This succession is perhaps most easily seen in the West 

 Indies in the action of the shield-scale fungus working on more or 

 less isolated trees. In lime plantations, it takes place in sections 

 of the cultivations rather than on individual trees. 



Several observers agree that, in the case of white fly control 

 in Florida, the parasites under favourable conditions, and without 

 artificial aid, become effective about every third year. 



It was noted above that in certain localities conditions are 

 so favourable to the spread of scale fungi that the matter may be 

 left to itself. What can be done in the districts not so favoured ? 

 Unless there is at some period of the year a season when the fungi, 

 if they are present, can be observed to become active, it is not 

 worth while to trouble about them. If they are not present at 

 all, it is probable, since they are so well distributed through the 

 islands, that the conditions are not favourable. Where they 

 have a period of valuable activity in the wet season, followed 

 by comparative scarcity in the dry, something may be done. It 

 will be found that, while they disappear from view in exposed 

 situations, they continue a visible existence in damp and sheltered 

 places. The spores of most species do not appear to be very 

 resistant, and it is probable that it is from such places that the 

 spread begins when conditions become favourable. By dis- 

 tributing the material thus available, or by taking material 

 from the earliest plants to become infested, it is possible, and has 

 often been definitely claimed, that the progress of the fungus 

 may be considerably hastened ; especially is this the case with 

 isolated trees. 



In Trinidad, a series of steam-heated cabinets has been 

 used for turning out the spores of the froghopper fungus Metar- 

 rhizium anisoplioe on a large scale, and these have been dusted 

 on the cane fields. The amount of fungus control in treated 

 as compared with untreated fields has not been demonstrably 

 increased and the practice is in abeyance or abandoned as being 

 too uncertain or indefinite in its results. 



Various methods are available in making use of natural 

 material. Branches from the fungus-infested tree may be 

 tied among the leaves of the tree to be infected. Leaves bearing 

 the fungus may be dipped in water and rubbed on the leaves 

 bearing the scales, or pinned in contact with them. The material 

 may be stirred up in water to wash off the spores, or ground up 

 and mixed with water in the case of leaves. 



