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 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 maj 7 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. 



