On the Value of Poison Bait for Controlling Cane Urubs. 13. 



It is proposed to investigate this question next season by studying 

 the imdergronnd tropic reactions of the larva, or, in other words, the 

 reflex acts or combination of such, induced mainly hy the moisture^ 

 temperature, and physical character of soils, and wliich are prol)ably 

 influenced in some degree by other comparatively ()l)scure forces of a 

 chemotropic or olfactory nature. It will be of interest to mention ia 

 this connection an important cage experiment conducted in ]\Iay (1916) 

 to discover whetlier grubs would eat this bait if it were closely sur- 

 rounded by cane roots. 



Larger eages holding 60 cubic inches of soil were used, and the 

 bait (about 2 square inches of leafage) placed just below a mass of 

 living roots, arranged so that the caged grub would encounter its natural 

 food first, and be obliged to pass among it to reach the poisoned leaf. 

 Twenty cages were treated in this way. ten with copper arsenate bait and 

 the remainder with arsenious acid, each enclosing a large third stage 

 larva of our Gray-back Beetle. 



Results revealed by subsequent examinations proved eminently 

 satisfactory in the case of the former arsenical, which in forty-eight 

 hours had occasioned a mortality of no less than 60 per cent., followed 

 by 90 per cent, in three days, and 100 per cent, in a week. The ten cages 

 containing white arsenie bait yielded 60 per cent, of dead grubs after 

 twenty days. 



The season is now too far advanced for further investigations 

 relative to the larval stage of cane-beetles, but this last experiment, and 

 indeed the results of previous research work as a whole, illustrate the 

 very deadly nature of arsenate of copper in undiluted form, and incline 

 me to think that it may ultimately prove to be the best insecticide for 

 our purpose. 



In the event of field experimentation next season being successful, 

 we may consider one phase of the cane grub problem as practicalh' 

 solved; but, unfortunately, in the present instance are dealing with an 

 indigenous insect that breeds in untold numbers over a vast portion of 

 Northern Queensland, and must remember that whatever form of control 

 may be adopted in the future, whether preventive or remedial, we cannot 

 eradicate this pest, but only hope, at the best, to effectually combat its 

 ravage.s on limited areas devoted to the cultivation of sugar-cane. 



NOTE BY GENERAL SUPERINTENDENT. 



In reply to question as to the possibility of the grubs attacking the 

 cow-pea roots and perhaps destroying the plant before it could be dusted 

 and ploughed under, Mr. Jarvis has supplied the following notes :— 



'• I think that although individual cow-pea plants might suffer from 

 grub attack, such damage would not be sufHcient to seriously interfere 

 with the experiment. 



