16 A STUDY OF NATUEAL METHODS OF 



27th'July — No. 12 was dead, blackened along the line of spiracles. 



9th August — No. 18 was dead ; Nos. 3, 7, and 17 were infected. 



21st August — No. 4 was infected on the back left leg. Check No. 20 

 was infected on the right front leg, which had gone black ; also Check 

 No. 23, which had the left hind leg black. Nos. 1 and 6 had succumbed 

 to fungus. 



Xofe — This infection in the checks was undoubtedly due to a lack 

 of care in][examining the grubs, for it would be an easy matter to infect 

 them from the hands. The pots were in a warm place on a table in the 

 sun, which probably accounts for the low mortality. 



25th August^ — No. 3 was dead of bacteria. No other changes. 



3(^11' August — Checks Nos. 20 and 23 were dead of fungus, following 

 the bacterial infection. 



4th September — No. 4 was black on the under side of the thorax. 

 Nos. 2, 9, and 10, dead of fungus. 



10th Sej)tember — The weather has been very warm. No. 4 dead 

 of fungus, following the bacterial infection. No. 11 dead of fungus. 



17thl September — Weather warm. No. 16 dead of bacteria. Check 

 No. 22 pupated. Nos. 7 and 17, no change, except that the infected legs 

 had dropped off. 



The experiment was discontinued at this point, since the weather 

 was too warm to get results with the disease. There were three checks- 

 and five of the grubs in the infected pots still ahve. 



Fourth Experiment. — 2nd August, 1920, nineteen healthy grubs from 

 Meringa fields were placed in nineteen pots of soil from the infected area, 

 at Greenhills. The soil was then made very moist, and covered to prevent 

 evaporation. 



5th August — No change ; this lack of mortality is evidently due ta 

 the 2^revailing warm weather, the pots being in the sun. 



9tli August — Two of the grubs dead of bacteria. The pots were 

 removed to a jilace under the laboratory, where the temperature was. 

 about 10 degrees cooler. 



21st August — Five grubs were dead of the fungus, and one of bacteria. 



25th August — Four grubs dead of fungus, and one of bacteria. 



27th August — Four grubs dead of fungus ; only two left alive. 



30th August — The last two grubs were dead of fungus. 



Concusions. — From the above experiments, it was quite evident 

 that low temperature and abundant moisture are most important factors 

 in the virulence of these diseases. The bacterial contagion was far less 

 destructive than Muscardine fungus, under the same conditions. Never- 

 theless, as noted above, these two diseases often go hand in hand, the 

 grubs dying by a complication of ailments. Often the h^gs of a grub 

 became blackened, one or more falling off — unmistakable syinptoms of 

 the bacterial complaint — then the grub would quickly succumb to the 

 fungus, his body becoming hard and cheesy, and, finally, turning green 

 as the spores developed. The fungus spores are exceedingly small ; 

 even when viewed under a microscope with a magnification oF 400 dia- 

 meters, they appear as exceedingly tiny oval bodies {Fig. 5). OrcUtiarily, 



