Parasites rather than phoronts: Teratorhabditis synpapillata nematodes reduce lifespan of their Rhynchophorus ferrugineus host in a life stage-dependent manner.

Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae) red palm weevils are often reported in association with different organisms including nematodes. The significance of this interaction and whether nematodes can influence their life-history traits is unclear. We collected Rhynchophorus ferrugineus red palm weevils at different developmental stages and locations in Tunisia, observed and dissected them in search for nematodes and other interacting organisms, established laboratory colonies and identified the nematodes associated with them, and conducted nematode-insect interaction assays to determine the capacity of the nematodes to influence their life-history traits. We observed Beauveria bassiana fungi in larvae, nymph, and adults; Centrouropoda and Uroobovella acari associated with the adults, and Teratorhabditis synpapillata nematodes associated with larvae and adults. Nematode-insect interaction bioassays revealed that T. synpapillata nematodes reduce the lifespan of the insect larvae in a population-dependent manner, but do not influence the lifespan of adults. Our study uncovers an important factor that may determine population dynamics of this important palm pests and provides evidence to conclude that these organisms establish a parasitic relationship, rather than a phoretic relationship.