A STUDY OF THE FACTORS OF CONTROL. 77 



;aetive ; at 4.30 p.m. the other two began to revive. The next day seven 

 had entered the soil, and one v;as fairly active on top, another was barely 

 moving, and the remaining one limp ; these last three died soon after. 



On 1st April ten more were removed at 2 p.m. ; eight of them were 

 I'igid on the surface of the soil and the other two limp and floating, 

 evidently dead. At 3 p.m. there was no sign of life, though some of 

 them had lost their rigidity. An hour later one was moving; this had 

 •entered the soil next morning, and two more were moving, but one of 

 these finally succumbed ; hence there were eight fatalities. 



2nd April another ten were removed at 11.30 a.m., and they were 

 mostly rigid. At 4 p.m. three of them were digging into the soil ; the 

 Temaining seven did not recover. 



The last ten were taken out of the water on 3rd Ai)ril, mostly limp, 

 and none revived. 



From the above we found that 30 per cent, of the grubs died after 

 a submergence of one day ; 30 per cent, after two days ; 80 per cent, after 

 three days ; 70 per cent, after four days ; Avhile they all succumbed when 

 submerged for five days. Hence we may safely conclude that an overflow 

 which flooded the fields for one or two days would only destro.v the 

 weaklings, while three or four days would begin to have a vital effect 

 ■even upon the strong, and none could withstand an inundation of 

 five days. 



These experiments have demonstrated that the grubs usually come 

 to the surface when the soil is flooded, and in a few cases, especially in 

 the younger stages, their bodies float, thus exposing the spiracles on the 

 upper side to the air. In such instances Mr. Dodd found that the grubs 

 do not succumb, even when in the water for five days; yet they would 

 be carried away by the current. 



Hence it would appear that it is rather hopeless to attempt to 

 drown the grubs hy irrigation, though those that w^ere too deep to get 

 out in time might succumb if the soil was kept saturated long enough. 

 There is no doubt, however, that irrigation would prove an important 

 factor in grub control in other w-ays, as will be taken up later on. 



Diseases^ are frecpiently of tremendous importance in the control oC 

 grubs, especially under unfavourable climatic conditions. Two distinct 

 diseases occur in our Northern districts, though, unfortunately, they are 

 quite localised. These are the green ]\Iuscardine fungus (MctarrJiizium. 

 anisoplw Metseh.) and a bacterial disease which is probably Micrococcus 

 idgrofaciens Northrup. 



Wherever these diseases were present they practically wiped out 

 the grubs, under the peculiar conditions which iirevailed during the 

 season of 1920; hence it would appear that we might ])rofitably assist 

 nature by inoculating all of our grubby fields by distril)utiiig the spore- 

 laden soil. 



Predatory Mammals which probably have a considerable bearing upon 

 the control of the grub-pest are the bandicoots (Pcrameles sp.), pouch 

 mice [Antcchinomys, Smintliopsis, Phascologalc), flying-foxes (Ptcropu? 

 sp.), and on most farms we find hogs, which are inveterate destroyer, 

 of grubs. especiall,v if the.v can be turned into the fields when a crop k 

 being ploughed out. Some dogs, too, have been observed following the 

 ploughs and eating the large grubs. 



* Since diseases and the following natural cheeks liave been fully discussed in 

 ^Bulletins Nos. 12 and 13, these important agents Avill be only summarised here. 



