SECTION IX. — THEORIES OF DAMAGE AND GENERAL PROBLEMS. 129 



It will be seen that with extreme drought the froghopper is dormant, 

 but so also are all its enemies. With a slightly increased supply of 

 moisture, the vermilion parasites will start to breed and so reduce 

 the number of eggs passing over the dry season. With dry weather in 

 the wet season, the froghopper increases rapidly while only the 

 vermilion parasite acts as a check. 



With moister weather the Green Muscardine and Syrphid Fly assist 

 the Vermilion parasites and the blight decreases, while greater moisture 

 again {e.g. heavy floods) has an injurious effect on the cane, on the 

 Vermilion Parasites, and probably also on the Green Muscardine 

 without affecting the froghopper which once more forges ahead. 



The results following from this suggested explanation are identical 

 with those found hy experience to occur. It is also possible, however, 

 that infestation is in some way directly related to the condition of the 

 cane as shown in the first column. 



PERIODICITY AND RELATIVE SIZE OF BROODS. 



Reference has been made to the way in which in some years the 

 third brood of frcghoppers is almost non-existent even after a serious 

 second brood. The same uncertainty exists with the other broods also. 

 Fig. 30 shows some of the typical variations in relative size of the three 

 conspicuous broods that have been observed. 



Fig. 30. 



Fig. 30 — General types of succession of tlie three chief froghopper broods in 

 different localities or in different years. 



A and B are two variations which occur in good years in both of 

 which the first brood is small, the second a little larger and the third 

 again smaller. Tlie year 1916 is a typical example of the first tj'pc and 

 the previous yeai' 1915 and the results observed at Caroni in 1919 

 (see Fig. 6) are examples of the second. 



C and D are typical sviccessious in bad years. The j-ear 1911 and 

 Caroni in 1908 are examples of the first, and certain fields (of B 847) at 

 Harmony Hall in 1919 of the second. The years 1912 and 1917 are 

 like D, except that tlie first brood was apparently larger than the third. 



