■S6 AUSTRALIAN SUGAE-CAXE BEETLES AND THEIE ALLIES. 



ialling-off of 4 to 6 tons of cane per acre. Along this line it may be 

 noted that W. T. Paget (23) stated that where Townsville manure was 

 used the grubs were bad, while there were none on the untreated land. 



It was my thought to make use of this attraction by mixing arsenic 

 with the fertiliser for the destruction of grulis. as had been done by 

 Mr. C. E, La Gaze, on the Herbert River, years ago (56) ; but in our 

 experiments the amount of poison used was evidently not sufficient. 



Irrigation, where it is practicable to apply, would undoubtedly have 

 a very beneficial effect as a control measure. In 1892, it was reported 

 (10) that Mr. E. G. Munro of Grassy Hill, writing to the "Queens- 

 lander," said that cane suffers from grubs only in dry and not in wet 

 land, and that in the latter the grubs were found to be in a dormant 

 state. Mr. ]\Iunro tested this matter by irrigating some stools, with the 

 result that the unirrigated cane died, whereas the irrigated stools had a 

 vigorous growth. Furthermore, the dry districts on the Lower Burdekin 

 do not suffer any injury from grubs, though the soil is a loose loam 

 perfectly adaptecl for them and the natural feeding-trees of the beetles 

 are plentiful. Possibly the constant irrigation which is resorted to there 

 is one of the important factors. 



(4) Where a crop has already been ruined, it is well to plough it 

 out as early as possible, so as to get the birds, &c., to destroy as many of 

 the grubs as possible, before they go down to hibernate. Naturally 

 these pests are usually centred under the stools; so these should be 

 broken up by harrowing and cross-ploughing, to get rid of the grubs 

 before cane is planted again ; for these large fellows iLsually take a 

 final nip at the young shoots, causing considerable expense for 

 xeplanting. 



ARTIFICIAL CHECKS. 



After reviewing the extensive list of natural and cultural checks 

 which retard the development of cane-beetles, one would think that none 

 would survive to require further repressive measures. It has been the 

 experience of workers in economic entomology, however, that nornuilly 

 the vast majority of the offspring of any insect are controlled by natural 

 means, only a very small percentage of the individuals of even our worst 

 pests requiring artificial repression. Insects are so prolific that man's 

 chances, for surviving even, would be small if he had to meet them all 

 single-handed. 



I have tried to make some estimate of the natural mortality among 

 cane-beetles at Greenhills by averaging the number of eggs and grubs per 

 .stool of cane at the beginning of their development, and comparing this 

 with the number of beetles just before they emerge. In no case have I 

 found more than 25 per cent, surviving; and where the Muscardine 

 fungus was active less than 2 per cent, escaped. Yet there are enough 

 to ruin hundreds of acres of beautiful cane, if not controlled artificially. 



Reviewing various factors in these treatments, I will discuss them 

 nnder the following divisions : — (1) Deterrents for grubs, (2) insecticides, 

 (3) collecting, and (4) removal of feeding-plants of the beetles. 



(1) For years it has been the hope of growers, as well as entomolo- 

 gists, to procure some substance which they could place in the soil to 

 drive the grubs away. Many experiments have been made in Queens- 

 land, dating back into the early nineties, using all sorts of substances, 

 but without success. Either the substance used had no effect, or, where 



