21 
expensive, and in addition, those of tin and paper cause unnatural 
rooting conditions. Mamey leaves and cylinders will always be 
used to some extent in small gardens for valuable plants, but their 
use on a large scale is past. 
Repellents. — The most satisfactory repellents are flowers of sul- 
phur and naphthalin flakes, though neither of these is completely 
successful where changa infestation is very severe. Dry sulphur 
drilled in with corn at the time of planting offers fair protection. 
Powdered naphthalin laid in parallel trenches J inch deep and 1 
inch from the seed row is an effective repellent as long as it retains 
its odor, usually about three to five days. Naphthalin so used did 
not hinder germination of corn or lettuce. The high cost and extreme 
volatility of carbon bisulphid make the use of this chemical out of 
the question. 
Kerosene emulsion is an effective repellent, but only at such 
strengths and in such quantities as to injure vegetation. Other ma- 
terials found to be either useless as repellents or injurious to plant 
life are lemon oil, mustard oil^ citronella, and creosote. Barrett (2) 
lists as unsuccessful repellents for the changa creolin, coal tar, lime, 
and tobacco (both as a dust and a stem mulch). Other writers have 
recommended heavy applications of "greasy manures" (22) and of 
kainit. 
Methods of planting. — Planting of sugar cane in a perpendicular 
or slanting position has solved the changa problem for this staple 
crop. When one or two eyes are left above ground, shoots are pro- 
duced out of reach of the changa. After the shoots have become suf- 
ficiently tough to resist further attack from the mole cricket, the 
sprouts may be partially covered over with earth. Leaving por- 
tions of the leaf-sheath over the eyes will also protect the tender 
sprouts from the changa. 
Hilling-up is often successfully employed to protect plants against 
the changa, advantage being taken of the insect's aversion to mak- 
ing its burrows up slopes. However, the writer has seen heavily 
infested fields where hilling-up had apparently had no effect. 
Clean cultivation of land in itself is not an effective means of 
protecting the crop which is to follow. It should be considered only 
as a step in preparing for the use of poisoned baits. Although the 
removal of all vegetation may cause the insect to migrate to other 
feeding grounds, migration takes place only after the absence of food 
for several days has made the pinch of hunger felt, and in a 
country where grasses grow so luxuriantly as in Porto Rico, keeping 
land clean for more than a week would be more costly than the result 
would warrant. In the laboratory the starvation period of both first 
stage and adult changas averaged about 22 days. In the field the 
presence of other insect food would lengthen this period. 
