On the Value of Poison Bait for Controlling Cane Grubs. 



Investigations were at once entered upon, and proved conclusively 

 that grubs of our Cane-beetle will readily devour the leaves of both 

 these plants. 



Finding cow-pea to be the more attractive, experiments were con- 

 ducted to determine the rate of decay of foliage of this legume when 

 buried at a depth of about 9 inches, and also with a view to rendering 

 its leaves still more palatable. Before attempting to study the latter 

 point it was necessary to undertake a long series of experiments, that 

 need n'ot be mentioned here, for the purpose of discovering an efficient 

 poison. Results for many months were unsuccessful, owing to the 

 extreme resistance of our cane grub to stomach poisons. Baits treated 

 with arsenical sprays of more tlian thirty times the strength usually 

 recommended for plant-eating insects failed to produce serious effects, 

 and for a time it seemed likely that this pest might ultimately be found 

 to be altogether proof against the cheaper forms of arsenic administered 

 in this manner. However, towards the end of February last I determined 

 to try the effect of dust sprays, applied, as a supreme test, at full 

 strength. 



Now, in a problem of this nature a poison to be suitable needs, in 

 the first place, to be very deadly, and at the same time sparingly soluble, 

 so as to withstand the action of heavy rains which Avould weaken and 

 soon lessen the efficiency of quickl}' soluble chemicals. Aceto-arsenate of 

 copper (Paris green) appeared to be more fitted for the purpose than 

 some of the other arsenical compounds, and although previous experi- 

 ments with it in 1915 had failed, 1 decided to give it another chance 

 under the most favourable conditions. Results secured last February, 

 1916, by the first of these tests proved very encouraging. 



Cow-pea foliage was sprayed on the upper surface with mill molasses 

 (1 pint to 3 pints water), and then dusted with the arsenical by sifting 

 it through coarse linen. The experiment comprised eleven cages, each 

 containing 20 cubic inches of fresh soil and a grub, nine supplied with 

 a poisoned leaf and the remaining two being controls with unsprayed 

 leaves, the foliage in each case being buried about 2 inches deep. An 

 examination made twenty-four hours later showed 70 per cent, of dead 

 larvae in various stages of decomposition, Avhich had between them con- 

 sumed less than three-quarters of a square inch of the poisoned leafage. 

 Subsequent examinations up to 10th February gave a mortality of 90 per 

 cent, in sixteen days. This important experiment was at once repeated 

 on 24th February, with seventeen treated and four control cages con- 

 taining first and second stage grubs confined with poisoned cow-pea 

 leaves, cut up in various forms as recorded by the following table : — 



