Reforestation of degraded lands in the tropics is one of the most important goals of ecological restoration. Restoration of montane wet forest is in progress at Hakalau Forest National Wildlife Refuge, Hawaii, using plantations of Acacia koa (koa), a canopy tree of montane wet forest. We used longhorned beetles (Plagithmysus claviger and P. varians) as indicator species to assess restoration. The beetles feed by boring into dead koa branches and are food for the endemic forest bird Hemignathus munroi. We quantified density of beetles in branches of koa from trees of 3 age categories: young plantations (3–8 y; 222 branches), older plantations (12–15 y; 212 branches), and canopy trees of intact forest (167 branches). We sampled by breaking dead branches into short pieces and counting the beetles within. Density of beetles was greater in canopy trees (4.89 beetles/branch) than in planted trees and was greater in older plantations (3.24 beetles/branch) than in younger plantations (0.90 beetles/branch). Beetles were clumped in distribution among branches (coefficient of dispersion  =  5.17). Mean basal diameter of branches in canopy trees (32.6 mm) was greater than in planted trees and was greater in older plantations (29.3 mm) than in young plantations (19.0 mm). In young and older plantations, branches that harbored beetles were larger than branches that did not, but in canopy trees there was no difference. Branch diameter had a positive effect on number of beetles per branch in all age categories. Koa plantations promote recovery of plant and animal biological diversity in degraded habitats formerly occupied by montane wet forest.