The New Guinea sugarcane weevil, Rhabdoscelus obscurus (Boisduval) (Coleoptera: Curculionidae), is an important pest of palms, ornamental nurseries, and sugarcane in the Pacific Islands. Without effective control methods, R. obscurus populations can cause major or complete loss of palm production in Guam and other Micronesian Islands. Moreover, R. obscurus has inflicted severe attacks on coconut trees on Guam. The role of monitoring is important in judging the dynamics of R. obscurus and recording area wide population trends. There is no precise research information available on the trap catch threshold levels relative to the damage caused by R. obscurus. Here we investigated the assessment of trap catch threshold levels and the potential for predicting R. obscurus larval damage by using adult pheromone trap captures. Spatial patterns of capture were studied in relation to subsequent larval damaged betel nut plants at various locations in Guam, United States, during 2010–2012. The generalized additive model was used to describe the effects of the treatment level (traps/ha), ranging from 0 to 12, and time on reducing the damage of R. obscurus to palms. We find that these two predictors are statistically significant, and the treatment level is demonstrated to be the crucial predictor for reducing the damage. There is no significant difference in effectively controlling the damage between the treatment levels of 9 and 12 traps/ha. At least 9 traps/ha is suggested for effectively controlling the damage based on results from the current study.