14 A STUDY OF XATURAL :\1KTH0DS OF 



We dug over 3 feet deep without finding any more. 

 A trench with five stools i^ave the following : — 



6 inches deep — Ten L. albohirtuiH, stage III., eight of them 

 killed by fungus ; one Anoplognathus, stage III. ; one 

 L. frenchi, stage III. 

 12 inches deep — Eight L. albohirtum, stage III., three of them 

 killed by fungus, and two killed by bacteria ; one L. 

 albohirium pupa ; four Anomala, stage III., in cells ; 

 one L. frenchi, stage III. ; one Camjisomeris wasp 

 cocoon. 

 18 inches deep — Two L. albohirtum,, stage III., one of them 

 killed by fungus : six Anomala, stage III., in cells ; one 

 L. frenchi, stage III. 

 24 inches deep — One L. albohirtum, stage III., pupating ; two 



Campsomeris wasp cocoons. 

 30 inches deep — One L. albohirtum, stage III., killed by fungus ; 



one Campsomeris wasp cocoon. 

 36 inches deep — One L. albohirtum pupa ; one L. albohirtum 

 beetle (1919) dead in cell. 

 This gives for the remaining grubs of L. albohirtum located in this 

 excavation : 20 per cent, killed by Campsomeris wasps, 40 per cent, killed 

 by fungus, and 5 per cent, killed by bacteria, hence, a total mortality of 

 65 per cent. ; of the remainder, 15 per cent, were pupating and 20 per 

 cent, were apparently healthy grubs. As indicated above, these figures 

 do not show the total mortality due to the diseases, because most of the 

 deceased grubs had disintegrated before the excavation was made. The 

 true percentage of mortality can only be determined by comparing the 

 remaining living grubs and pupae with the average number that were 

 there before the epidemic commenced. Since the original infestation 

 was well over 100 per stool, and at the time of this excavation it was 

 reduced to less than two per stool, we must conclude that fully 98 per 

 cent, had succumbed to these various death-factors. 



Further Experiments with these Diseases in the Laboratory. 

 In order to note more closely the conditions under which these diseases 

 were effective, I started a number of experiments in pots of soil in the 

 laboratory. By this means our field observations were thoroughly 

 confirmed. 



First Experiment. — On 10th July, 1920, three pots Avere prepa cd 

 with Greenhills soil, and three healthy grubs were placed in each. Pots 

 Nos. 1 and 2 were each inoculated with a grub that had succumbed to the 

 bacterial disease, the bodies being soft and black. Pot No. 3, no inocu- 

 lation, except what might oc^cur naturally in the soil. 

 13th July an examination was made, finding — 

 Pot No. 1 — Two grubs dead and black, one alive. 

 Pot No. 2 — One grub dead and black, two alive. 

 Pot No. 3 — One grub dead and black, two alive. 



Note — In two cases the dead grubs were on top of 

 the soil, just as 1 had observed in the field. 



