The objective of this study was to determine the in vitro susceptibility of weevil adults (Cosmopolites sordicus Germar) to infective juveniles (IJ) of Heterorhabditis amazonenesis Andaló et al. (Cuban strain HC1). The adults were collected in the field with sandwich and modified disc traps and kept in quarantine in the laboratory until their use in the tests. The insects were inoculated with suspensions of infective juveniles at the dosage of 125, 250, 500, 2500, and 5000 JI.ml-1. Controls without inoculation were included. Mortality was evaluated from 12 hours to 21 days after inoculation. Lethal dose values (LD50, DL90) and lethal times (LT50 and LT90) were determined through Probit Analysis and the percentage of mortality by performing an Variance Analysis. The weevil adults killed by the effect of the nematodes became stiff and hard, maintained coloration and shrank their legs. The LD 50 and LD 90 determined were 1872 and 6061 IJ / ml-1, respectively. The LT values estimated using the concentration of 5000 IJ / ml-1 for the control of 50 and 90 % of a population of C. sordidus were 17 and 28 days, respectively. The highest percentage of mortality was 86.7 using the highest dose at 21 days