SECTION IX. — THEORIES OF DAMAGE AND GENERAL PROBLEMS. 131 



In considerine; possible causes it must be remembered that Trinidad 

 is not alone in this condition. Demerara has just suffered a very severe 

 attack from a fro£;hopper previously unrecorded as a serious pest, and 

 other countries (Cuba, Colombia, etc.) will be found mentioned in Section 

 IV as having suffered more severely of recent years. 



It is thus probable that some general influences are at work in 

 addition to special causes that apply to Trinidad. 



Two suggested causes are referred to on p. 18. These are the 

 introduction of the mongoose and the introduction of seedling canes. 



(a) The mongoose has been fully discussed in Section VI p. 87 and 

 the conclusion arrived at was that, although undesirable, it could not be 

 considered as one of the important causes of the recent spread. 



(b) The question of the resistance of varieties is dealt with on p. 119 

 of the present report and more fully in a previous report ^Williams 1919 

 D.) devoted to this subject. There is no evidence to show that the old 

 Bourbon cane is more resistant to froghopper than many of the seedlings 

 now in cultivation. Some of the latter are indeed distinctly more 

 resistant than the Bourbon. 



Other factors that have to be taken into consideration are as follows : 



ic) The injurious effect of continual use of artificial manures 

 (sulphate of ammrniia and nitrate of soda) on soils which are deficient 

 in lime, as are most Trinidad soils. 



It is probable that the acid condition of so many of the soils in the 

 old sugar districts of the island has been aggravated by this practice, 

 and the resulting poor condition has been favourable to the multiplication 

 of the froghoppers. 



[d) The working out of the land by continual cane cultivation, 

 frequent burning of trash and insufficient use of pen manure has had an 

 injurious effect on the physical condition of the soil with similar results. 



(e) The spread of cultivation has had an injurious effect on the lizards, 

 birds and other animals which tend to keep down pests, and at the same 

 time the larger areas under one crop make the continuance of pests which 

 feed on that crop simpler and more certain. 



if) The rise of the study of economic entomology, and the greater 

 interest taken by planters in diseases has resulted in more accurate 

 recording and more careful search for their causes, since they are no 

 longer looked upon merely as "acts of God." 



The general increase of insect pests in many tropical countries of 

 recent years is part of the wider influence of the spread of civilisation, 

 population, communication and cultivation in places that have not 

 worked out for themselves reliable rotational methods of agriculture to 

 combat the disadvantages inherent in man's artificial method of planting 

 the same crop on large areas of land at frequent intervals. 



