1. A root-boring caterpillar has been found in Puerto Rico in the soil around sugar cane roots which has been named the sugar cane root caterpillar, Perforadix sacchari new genus and species (Pyralididae, Endotrichinae). It had been previously reported as Sufetula grumalis Schaus (Pyralididae, Pyraustinae) and specimens under that name from Puerto Rico and Santo Domingo are to be found in the collection of the U. S. National Museum in Washington. 2. In captivity, the larvae will also feed on the roots of corn, bamboo and Gynerium sagitattum, but in nature no indication of the work of this insect has been found on the roots of these plants. 3. In the early instars the caterpillars feed on the very tender roots or in their absence may tunnel in the cortex of the mature roots of sugar cane. The later instar caterpillars tunnel in the thick succulent tips of the tender roots. 4. The damage is cumulative. As the plantation grows older the number of caterpillars and the amount of injury increases. The injury may not show above ground but probably it causes always some reduction in yield and shortens the duration of the plantation. Upon the advent of dry weather and when the soil conditions are unfavorable for the production of new roots, the destruction of the root-tips may become in some localities the limiting factor in sugar cane growing. 5. The distribution of the caterpillars is not uniform in any plantation, and furthermore they seem to migrate from one plant to another in search of fresh root tips. As the soil also varies within any particular field, the root injury showing in the parts of the plant above ground, is not uniform. Scattered stools or patches of stools will dry out while the rest of the plantation may be uniformly green. 6. As a rule, when the soil conditions are proper for the sugar cane plant, although the injury to the roots may be abundant, it does not show above ground. 7. The root injuries produced by the younger caterpillars may he confused with those produced by other soil animals, but the tunneling in the larger roots made by the older caterpillars and the piles of whitish excrement thrown out of them are characteristic and unmistakable. 8. Soil fumigants have so far proved impractical, but the cultural practices recommended by Earle for "root disease" would make it possible for the plants to keep up a constant production of new roots and to produce satisfactory yields in spite of the injury caused by the root caterpillar. 9. Other new root pests of sugar cane whose injuries are found associated with those of the root caterpillar are the Symphylid, Hanseniella sp., the bristle-tails, Nicoletia and Lepisma spp., and the sow bug, Philoscia culebrae Moore.Resumen en español.