4 MONTHLY NOTES ON GEUBS AND OTHER CANE PESTS". 



place a sufficient value upon his own experience, especially when he is 

 asked to sit down and write it out. I onh^ got two replies to the ques- 

 tions, but these contained so many suggestions that it is a pity that 

 they could not have been multiplied by hundreds. 



Much of the information in the following pages, dealing with control 

 measures, is credited to experienced growers in the various districts that 

 I have visited ; and they have my grateful appreciation, for they have 

 enabled me to verify more quickly the several lines of treatment that I 

 have suggested in my earlier reports : — 



CANE GRUB INVESTIGATION, AUGUST, 1917. 



Though Ave have been handicapped to date by a lack of trans- 

 portation facilities, we have managed to get about somewhat, making 

 observations with regard to the various factors determining the degree 

 of grub infestation in the region about Gordonvale. 



The tremendous importance of the problem impresses one at once 

 upon viewing the great areas laid waste in districts like Meringa or 

 GreenhilLs. Apparently there is no easy road to success in combating 

 such a pest. Introduction of parasites will probably be of little avail, 

 since we are here dealing with native insects. It is a well-understood 

 fact that introduced parasites have only been used successfully against 

 introduced pests. The fact of the matter is, we already find a number 

 of parasitic and predaceous insects working against the grubs, but they 

 are unable to show any marked results because they are themselves 

 attacked by other parasites. There are, however, bacteria and parasitic 

 fungi doing efficient work in some fields, especially under proper con- 

 ditions of moisture, &c. Our excavations at Greenhills would indicate 

 that approximately one-third of the grubs succumb to these organisms. 

 "We have not yet been able to determine how widely these friendly agents 

 are distributed in the infested districts ; but they certainly lend them- 

 selves to artificial propagation and transplanting, so that no field needs 

 to be without them. 



In testing the soils of bailly-infested fields, they were all found 

 to be very poor in humus, and usually contained no lime — two factors 

 which would appear to be of vital imi)ortance to the growth of sugar- 

 cane in a grub district. First, the main food of the grubs is decompos- 

 ing organic matter in the soil, which, if it is lacking, forces them to 

 feed upon living roots of plants. Secondly, lime not only improves the 

 character of the soil by hastening the humification of plant tissues, and 

 making it possible for leguminous plants to store up a cheap and abun- 

 dant supi)ly of nitrogen, but its action is also very favourable to the 

 development of the fungous pai-asites. It is a Avell-known fact that 

 neither organisms of decay nor disease-forms will develop well in acid 

 soils — /.(., soils containing no lime. 



