Rhynchophorus ferrugineus (Olivier; Coleoptera: Dryophthoridae) is a pest of many crop and ornamental palm tree species in subtropical regions worldwide. Larvae tunnel and feed unseen in the trunks, ultimately causing irreparable harm and killing the palm. Beauveria bassiana (Balsamo-Crivelli; Hypocreales: Clavicipitaceae) Vuillemin is under evaluation as a biological control agent for R. ferrugineus management but its effects are difficult to monitor under field conditions except by acoustic methods. Older (>30 d) larvae treated with B. bassiana display statistically significant reductions in acoustic activity in semi-field studies, but activity of younger larvae has been more difficult to analyze due to their short-duration cycles of increasingly active and then less active feeding and movement, followed by inactive molting. A procedure was developed to characterize effects of B. bassiana treatments by subdividing long-term recording periods into activity cycles. Treatment effects were compared within and across cycles. The procedure demonstrated statistically significant differences among acoustic activity rates over time for 15-d-old larvae exposed to control, 10⁴, or 10⁸ conidia ml^–1B. bassiana treatments. The results suggest that acoustic technology has considerable utility for monitoring of larval development and for evaluating efficacy of pest management treatments in environments where the targeted insect pests are hidden from view.