GREYBACK CANE BEETLE, LEPIDODEEMA ALBOHIRTUM. 27 



As further evidence in this matter, it is well known that grubs do not 

 usually damage the cane planted on newly opened-up scrub land, which 

 is proliably due to the fact that this land is rich in a supply of humus 

 accunmlated from its rank growth of vegetation. And, again, the same 

 may be said of the soil on river-fiats. The crops on new forest land, on 

 the other hand, frequently suffer right from the start, for such soil is 

 poorer in organic matter, which is largely due to the annual fires that 

 pass through these lands. 



Normally there is little lateral movement of the grubs in the soil, 

 as long as they are able to find sufficient nourishment right under the 

 stools of cane, a fact which is especially true during dry weather. I refer 

 to this matter because growers liave frecjuently told me that as soon as 

 the rains ceased they could notice the advance of the grubs across the 

 fields, by tlie yellowing of the tops. This apparent advance, however, 

 is not due to a migration of the grubs. 1)ut may be explained by relative 

 infestation. That is to say, the parts of the fields near the feeding-trees 

 are usually more heavily infested, and hence become yellow soonest : while, 

 as M'e have demonstrated, as the number of grubs per stool varies 

 inversely with the distance from the feeding-trees we would naturally 

 find that the cane planted farther away would be slower to succumb to 

 drought, being less injured by the grubs. 



There is no question, however, that the grubs have ability to move 

 about in the soil, where they have occasion to do so, that being their 

 natural element. Nevertheless, when taken out of the soil, progress is 

 almost out of the question. They squirm about, l.ving on their sides, and 

 try to get back into the soil as soon as possible. Hence there is no reason 

 to believe that they voluntarily come out on the surface, even in wet 

 weather, in order to move from one place to another. 



To learn something of the movement of the third-stage grubs in very 

 moist, red volcanic soil, I experimented somewhat during January, 1918, 

 at Meringa. Single grubs were placed at different points on the surface 

 in a part of the field that was not infested, and the places where they 

 entered the soil was marked. After twenty-four hours I dug until I 

 located each of them, finding that in no instance had they moved more 

 than 12 inches laterally, though one had descended to a depth of 9 inches. 

 This soil was without roots, with little organic matter, so there was every 

 incentive to travel in search of food. 



Toward the end of their feeding period, in ]May or June, the third- 

 stage grubs become very j^ellow. especially on the thorax, because of the 

 great amount of fat they have stored up to last them over the several 

 months wliich they pass in the resting stage in the pupation chamber. 



The P»pf/._When the cold nights begin, therefore, if thev have 

 reached this stage in their development, they begin their descent", going 

 perpendicularly deeper and deeper; and if the soil is not too hard there 

 IS apparently no limit. Girault (57) found them as deep as 4 feet; and 

 on several occasions growers have reported to me that they found them 

 considerably deeper— in one instance 6 feet. In none of our excavations 

 have we gone deeper than 4 feet ; yet, in the loose, red volcanic soils. M-e 

 frequently located the pupating grubs at a depth of 3 feet to 3 feet 

 6 inches. In fields with heavy clay subsoil, on the other hand, the grubs 

 do not go down so far; in fact, it is not uncommon to find them pupating 

 almost at the surface. This is undoubtedlv largelv due to the moisture 

 ■content in such poorly drained situations. While it has been found that 



