On the Value of Poison Bait for Controlling Cane tirubs. 9 



Tlie experiment shown in Ta])lr' II. Avas repeated on 12th April with 

 sixteen grubs, but using leaves that had been similarly treated on 22nd 

 ^larch and left for three weeks lying in damp soil. The result was a 

 mortality of 45 per cent, in twenty-one days, demonstrating that leaves 

 (lusted with copper arsenate and tloui- (1-3 formula) retain a marked 

 degree of etfeetiveness after remaining in the ground for about five 

 weeks. 



WHITE ARSENIC BAIT. 



Having secured such good results with arsenate of copper, I decided 

 to experiment with arsenious acid, commonly known as white arsenic, 

 whieli, although more soluble in water than Paris green, is much cheaper, 

 ;iiid has the additional advantage of being very conspicuous in the fiehl. 



In the first experiment, started 25th February with six infected and 

 two control cages, the arsenical was applied in undiluted form as a dust 

 spray, with most encouraging results. It was sifted through butter cloth 

 on to cow-pea leaves moistened with null molasses solution (1-3 formula), 

 and 2 scjuare inches of the poisoned leafage placed in each treated cage 

 enclosing a second stage grub of albohirta in 20 cubic inches of soil. A 

 nu)rtality of 100 per cent, was obtained in ten days, the amount of 

 poisoned leafage eaten collectively by the six dead grubs being about 

 1 square inch. Controls remained perfectly normal throughout. This 

 experiment was repeated on 14th iMarch with foliage that had been 

 poisoned on 25th February and buried for eighteen days between rows of 

 sugar-cane. These leaves when dug up were in a semi-rotten state, and 

 more or less interlaced by slender cane roots, that appeared to be deriving 

 nourishment from them. Portions of this decaying vegetation were then 

 placed with cane grubs in five cages of soil, and by the end of fourteen 

 days had caused a mortality of 100 per cent., proving that this arsenical 

 retains its efficiency underground for at least a month. 



WHITE ARSENIC versus PARIS GREEN. 



Desiring to ascertain the effect of diluted white arsenic, an experi- 

 ment was started on 24th March identical in construction with that given 

 in Table II., the only difi'erence being the employment of this arsenical 

 in the place of Paris green. 



Detailed results need not l)e tabled here, it being sufficient to state 

 that after a lapse of three weeks the death rate did not exceed 3:>-:)() per 

 rent. 



Compared with eoi)pei- arsenate, the elfeet obtained may be sum- 

 marised thus: — 



raris Green (1-3 fornuila) — 



In one week killed oS per cent, of grubs. 



In two weeks killed 75 per cent, of grubs. 



In three weeks killed 91-60 per cent, of gmibs. 



WJilh Arsenic (1-3 formula) — 



In one week killed 16 per cent, of grubs. 



In two weeks killed 25 per cent, of grubs. 



In three weeks killed 33-30 per cent, of grubs. 



