SECTION VIII. — FACTORS INFLUENCINfi IJI.KillT PKEVALENCI.:. 103 



Fig. 25. 



Tlie close siuiil;irity between 

 the periods, confirms Kershaw's 

 observation that the egg 

 ;estivates at a very early period 

 in its development. 



The a])ility to foretell the 

 dates of the broods is of great 

 practical ini])ortauce, and will 

 be considerably more so if any 

 direct method should be 

 adopted of combating the pest 

 in the field. 



Ordinary variations in the 

 rainfall dnring the wet season 

 do not appear to have any par- 

 ticular effect on the adult or 

 nymph fi'oghopper, the latter 

 being particularly well protected 

 by its frothy covering from 

 temporary extremes of moisture 

 and drought. 



The continuation of the rain- 

 fall late in the year does not 

 have the same effect in pro- 

 ducing late broods that might 

 be expected. For some 

 unknown reason most of the 

 eggs laid by the third brood do 

 not seem to hatch until after 

 the dry season. 



Urich however (Bull. Dept. 

 Agr. XTII. 1914, p. 102) says 

 that "the comparatively damp 

 peiiod at the end of 1912 [as 

 compared with 1911] caused 

 u^a:iy eggs th;it would have 

 sestivated to hatch out and the 

 nymphs either did not coniplete 

 their transformations or were 

 attacked by natural enemies." 



Fig. 25 — Diagram showing tlie relation between the conimeucement of the wet 

 season and the dates of the principal broods of froghoppers from 1906-1919. Ther 

 lines between the crosses represent the commencement of the wet season. The lines 

 between the arrow heads the time of the successive broods of adults. 



Doubtful fourth broods have been recorded in 1908 and 1917 and 

 may occur in isolated localities more frequently. 



(2) Effect on the Enemies of the Froghopper. 



From the captures of adult vermilion parasites during the dry 

 season, it would appear that this insect can continue breeding at a 

 much lower degree of moisture than that required by the froghopper ; it 

 is also very probable that sudden heavy downpours have an adverse 

 effect on it as on most small parasites. 



During the dry season the Syrphid fly disappears in the cane 

 districts, but this may be a direct result of the absence of froghopper 

 nymphs. On the other hand the maggot of the Syrphid lly has to travel 

 along the ground from one mass of froth to another and under dry 

 conditions this would not be easy. 



