12 A STUDY OF XATUEAL METHODS OF 



have learned that the mortality is increased by lowered temperature and 

 abundant moisture, it would appear that we might easily add to the 

 destruction in the field by irrigation, especially after the cool weather 

 sets in, which is normally the dry season. 



During the survey we also found many grubs that had died of some 

 bacterial disease, which occurred in the same areas with the fungus. 

 The locations of this second disease were indicated with a B on the sketch 

 of the estate. Many of these dead grubs were also found on the surface. 

 By digging under such stools specimens were found presenting all stages 

 of the disease. This infection usually appears at one of the spiracles, 

 or in the membrane between the segments of one or more of the legs ; 

 in the latter case, the affected appendage soon drops off and the disease 

 rapidly progresses upward into the body. The affected parts have a 

 peculiar shiny black appearance, which coincides with that described by 

 Zae Northrup* who gave the name Micrococcus nigrofaciens to the organism 

 causing the disease ; this friendly organism was found to be well distri- 

 buted in the United States. Finally, at death the body becomes very 

 soft and black all over (Fig. 3), totally different in appearance from 

 specimens that have died from the fungus (Fig. 4), the latter being hard 

 and cheesy, with a soft grey-green covering of spores. 



Naturally, such macerated specimens quickly decompose in the soil, 

 and it is almost impossible to find them after a few days. This fact helps 

 to account for the way that the grubs so suddenly disappear, as if by 

 magic in some instances, when climatic conditions are just right. The 

 remarkable disappearance of the grubs at Fairy mead, in 1909, is a case in 

 point. I have discussed this matter with Mr. Howe, Manager of the 

 Mulgrave Central Mill, who was located at the Lynwood Estate at that 

 time, and who made a careful study of the mortality of the grubs. f From 

 all that I can learn, the mites which appeared in such numbers on the 

 sick grubs were only an after effect, the real cause of death being apparently 

 due to a bacterial disease similar to the above. Mr. Howe also informed 

 me that that district had since been free from grubs for years, but that 

 they had , ust begun to give trouble again. 



Due to favourable rains, these diseases continued active in the 

 field right through July, and even on 3rd August we found considerable 

 evidence of them at Greenhills. Digging near the quarters, in one of the 

 worst-infested locations, we found the following : — 



12 inches deep — One L. frenchi, stage III. ; two L. frenchi, 

 stage II. ; one L. albohirtum, stage III., killed by fungus. 



18 inches deep — One Anotnala, stage III., in cell ; one L. 

 albohirtum pupa in cell ; one L. frenchi, stage III., in cell. 



24 inches deep — Three Anomala, stage III., in cells ; one L. 

 frenchi, stage III., in cell. 



* Mich. Tech. Bui. No. 18. 

 ■^ Aust. Sugar Journ., T., 65. 



