The trend in the relative populations of Oryctes rhinoceros (L.) in two areas of the Gazelle Peninsula, New Britain, was studied by trapping adults searching for breeding sites. In a high rainfall area with 10-year-old palms and many possible breeding sites, there was a large initial population of beetles which declined over the next three years with the gradual disappearance of the breeding sites; weekly catches were higher when the undergrowth in the trapping area was slashed, and to some extent also at new moon; catches were depressed by heavy rain. The ♂/♂ sex ratio was 0·31; all females had mated and had mature eggs in the lower ends of the oviducts. These results were compared with those from a low rainfall area with 70-year-old palms and dispersed breeding sites. Catches were generally lower; they showed no long term trend and were not related to slashing or weekly rainfall, but were inversely related to the number of rainy days per week.