ACOUSTIC DETECTABILITY OF RHYNCHOPHORUS CRUENTATUS (COLEOPTERA: DRYOPHTHORIDAE)

The palmetto weevil, Rhynchophorus cruentatus (Fabricius), is a pest of cultivated palms in Florida. The larvae of this species and 2 other important Rhynchophorus pests, R. ferrugineus (Olivier) and R. palmarum (L.), feed internally and cause structural damage to palm fronds, trunks, and offshoots. Often, infestations are not detected until the tree suffers irreparable damage. Acoustic methods used previously to detect R. ferrugineus in field environments were applied to investigate detectability of early instar R. cruentatus larvae. Sounds from neonates inoculated into palm fronds were recorded for 120 s periods at 7-day intervals for 56 days in urban (exposed) and acoustically shielded (enclosed) conditions that might be encountered when screening offshoots for sale or transportation. The sounds were classified by automated spectral analyses into multiple categories, including vehicle noise, bird calls, and broadband, 0.3-3-ms larval sound impulses. Because spectral characteristics alone are not always reliable identifiers of larval signals in wood, the analyses also identified trains of 6 or more closely grouped larval impulses called bursts to help classify fronds as infested or uninfested. Larval bursts were produced at sufficient rates to classify inoculated fronds correctly each day of testing, although molting and resting behaviors resulted in the absence of bursts in 6-50% of individual, 2-min recordings. The rates of larval bursts were not significantly different in paired comparisons of recordings obtained from the same frond on the same day under urban and shielded conditions, which suggests that bursts are useful as indicators of Rhynchophorus infestations in a variety of conditions.