Tubers of Irish potato Solanum tuberosum L. - harvested in soil rich in organic matter along the Paraiba river in the State of São Paulo, are severely damaged by a Coleopterus larva - Scarabxidas - Dyscinetus planatus (Burm., 1847), known by the local name of "bicho bôlo". Potato tubers from eight commercial varieties harvested in trials carried out in the Taubaté region were examined in order to verify the extent of damage caused by the "bicho bôlo" larvae. It was verified that all varieties were susceptible. The percentage of damaged tubers was variable in two years of observations ranging from 3 to 14% in 1946 and from 20 to 44% in 1951. Data are presented about the biology of the insect, its occurrence in the State of São Paulo and its natural enemiee. It was verified that one particular fungus, not yet identified, was a potent natural enemy of the "bicho bolo" larvae. Preliminary results of one experiment are presented on the control of the pest by the use of D.D.T. in the soil at several concentrations.