Ultrastructural Morphology of the Red Palm Weevil (<i>Rhynchophorus ferrugineus</i>) and Its Associated Phoretic Invertebrates: A Scanning Electron Microscopy Study

ABSTRACT The red palm weevil ( Rhynchophorus ferrugineus Olivier) is a highly destructive pest that severely threatens palm trees due to the feeding activity of its larvae and adults. The concealed lifestyle of R. ferrugineus , with larvae developing inside palm trunks and adults tunnelling through tissues, has led to specialised morphological and physiological adaptations that facilitate their survival and proliferation. Understanding these adaptations is critical for developing effective management strategies. This study investigates the external morphology of both larval and adult stages, along with their sensory structures, using scanning electron microscopy (SEM). The analysis revealed distinct sexual dimorphism, particularly in the structure of the rostrum and sensory organs. Additionally, the mouthpart morphology of larvae was examined, highlighting adaptations suited for wood boring. Various sensillae were identified across both sexes, including infrared sensilla, spicules, and spiracles elevated above the thoracic and abdominal surfaces, surrounded by protective spines. Five distinct morphotypes of sensillae were characterised: multiporous peg sensillae, sensilla coeloconica (Types I, II, III), bifid trichoid sensilla, and sensilla trichoidea (Types I, II), with no significant differences observed between males and females. Furthermore, SEM analysis documented the presence of phoretic mites, specifically deutonymphs of Uroobovella sp., on both male and female weevils and pupae. Notably, fungal spores associated with these mites were detected, suggesting a potential role in pathogen transmission that may contribute to palm tree deterioration. These findings provide valuable insights into the morphological adaptations of R. ferrugineus and the ecological interactions that may influence its impact as an invasive pest.