CONTROL FOR WHITE GRUBS. 11 



3 feet. The soil was rather dry and crumbly, so that the dead grubs were 

 easily broken up and difficult to discover— only the chitinous head-shield 

 remaining for a time after the decomposition of the soft body. 



Furthermore, experiment demonstrated that the diseased grubs 

 often came to the surface before dying, and, hence, were easily removed 

 by predators— ants, ground beetles, mammals, and birds. On one 

 occasion I watched a flock of fully 500 ibises assiduously probing about 

 the grubby stools ; and in almost every case the soil was dug up at the 

 roots by the omnivorous bandicoot in his search for the grubs. With 

 all these grub -destroyers at Avork it is not hard to understand the rapid 

 disappearance of the pest. 



Though I had often found grubs destroyed by the Muscardine fungus 

 at Greenhills and elsewhere, as noted above, I had never observed such 

 remarkable mortality. Under normal conditions they go down to hiber- 

 nate in March or April, before the cool weather sets in ; and they appear 

 to be fairly immune to diseases when they are thu=; located deep in the 

 moist subsoil. In our experiments it was noted that mortality increased 

 with the lowering of the temperature, and wa, also stimulated by the 

 addition of moisture ; hence, the heavy death-rate in the field, with this 

 combination of factors, is just what we might expect. 



During the time that the Muscardine fungus was most virulent, 

 following the chilly rains of early July, it was very conspicuous in the 

 soil. The greenish- white mycelium extended out on every side of the 

 grub for 2 inches or more. In some cases this mycelium had attached 

 itself to the underground portions of the cane, wherever the diseased 

 grub had been in contact ; in fact, we often discovered the disintegrated 

 grub by seeing the grey-green spores or mycelium on some portion of the 

 root system. 



By the middle of July the percentage of dead grubs had greatly 

 increased. The ibises were in the infested fields in hundreds, gathering 

 up the sick larvae within reach of their long beaks. In digging we found 

 many stools in which every grub had succumbed (100 per cent.). 



Following on this important evidence, I started a careful survey 

 of all the infested fields at Greenhills, to earn if this valuable disease 

 was distributed throughout the plantation. This was done by digging 

 out numerous stools in each of the infested fields, the result being indicated 

 on the plan of the estate by an X for fungus and for none. By this 

 method I developed an interesting discovery — the fungus appeared to 

 be well distributed in all of the areas regularly attacked by grubs {i.e., 

 those deeply shaded on the sketch), but we were not able to find it outside 

 of this well-defined region, especially where the pest in its erratic flight 

 had caused the devastation of fields that had usually been immune 

 {i.e., the portions stippled on the sketch). 



Apparently, the disease spores persist in the soi where they have 

 once been introduced, and continue from year to year, ready to bring 

 about an epidemic when conditions are favourable. Therefore, since we. 



