Acoustic signal applications in detection and management of Rhynchophorus spp. in fruit-crops and ornamental palms

Rhynchophorus ferrugineus (Olivier) (Coleoptera: Dryophthoridae) is an economically important, internally feeding pest of ornamental and fruit-producing palms in many subtropical regions. A related weevil, Rhynchophorus cruentatus (Fabricius) (Coleoptera: Dryophthoridae), is an internally feeding palm pest in the southeastern USA. Acoustic methods for detection of early instars hidden in palms in field environments have been investigated for both species. Acoustic methods also have been used to examine the effectiveness of physical, biological, and other control treatments. This report addresses several physical, physiological, and behavioral factors that influence the spectral and temporal patterns of sounds produced by palm weevil larvae under different laboratory and field experiment conditions, which must be considered carefully in interpreting larval sound production. Such factors include the leakage of fluid from the palm tree tissues into tunnels scraped out by larvae as they move and feed within the tree trunk, as well as occurrences of molting between periods of feeding activity, and frequency-dependent damping that distorts signals as the distance between insects and sensors increases. Methods are discussed that combine effects of environmental, physiological, and behavioral variability to facilitate reliable interpretations of Rhynchophorus and other insect larval acoustic activity in hidden environments.