10 A STUDY OF NATURAL METHODS OF 



Unfortunately, results from the Greenhills fungus plot were also- 

 inconclusive. This was largely due to the fact that during the 1920 seasorL 

 this disease became a real epidemic extending practically throughout 

 all of the fields covered by the shaded area in the sketch. The cane- 

 treated, :'n a grubby field just north of the quarters (the cluster of black 

 rectangles near the horse paddock), gave no greater percentage of mortality 

 than any of the adjoining untreated blocks ; hence I could draw no. 

 conclusions in this particular experiment. 



Epidemic at Greenhills during 1920. 



Since the grubs did not hatch until fully two months past their 

 reoular season, they were compelled to continue their activities among 

 the cane roots well into the winter, before descending into the lower 

 levels of the soil to hibernate. This unusual procedure was their undoing ; 

 for, wherever there were fungus or bacterial spores in the soil, fully 98. 

 per cent, of the grubs succumbed to these diseases before they were ready 

 to pupate. This fortunate devastation in their ranks resulted because 

 they were subjected to a continuation of a peculiar season. Unusual 

 rains occurring during the cooler months of May, June, and July developed 

 ideal conditions both for the activities of the fungus and other death- 

 dealing organisms, such as bacteria, &c. 



Even as early as March I began to find grubs that had been killed 

 by the fungus, and by the middle of June there was a real epidemic, for I 

 then foimd 37i per cent, of them succumbing to it. This was the greatest- 

 mortality that I had ever observed, up to that time. 



Nevertheless, by 1st July I found this average greatly increased. 

 The first stool that I examined in the field just north of the quarters; 

 had twenty-six grubs, all third stage L. albohirtum ; eighteen of them 

 were already dead and mouldy with the Muscardine fungus, i.e. 70 per 

 cent, mortality among the number located ; and undoubtedly many 

 had already disintegrated, for these stools formerly had an average of 

 100 grubs or more per stool a short time before — in fact, in one case,. 

 I found 134. 



About 9th July weather conditions became rather dry, and there- 

 was a consequent decrease in the death rate. Then, too, those that had 

 been dead for a short time were rapidly breaking up into humus, so that 

 they were very hard to locate when digging. Nevertheless, there was a 

 marked decrease in the number of grubs in the soil on every side. At 

 first I supposed that they might have gone down to hibernate, but digging- 

 failed to disclose any of them deeper than 12 inches. Where, a short 

 time before, the grubs had been exceedingly numerous, going m'cU over 

 100 per stool, it suddenly became difiticult to find more than about four. 

 For example, a typical stool gave — 2 to (5 inches deep, two alive and 

 one dead by fungus ; 6 to 12 inches deep, one alive, one dead by fungus, 

 one sick with black spots on skin indicating a bacterial disease, and one 

 dead, spotted and very soft — undoubtedly due to bacterial disease- 

 No grubs were found deeper, though we excavated to a (h^ptli of over 



