Natural enemies of Rhynchophorus ferrugineus and Paysandisia archon

Biological control of insect pests consists of the beneficial action of entomophagous predators and parasitoids, and entomopathogenic microorganisms (protozoa, nematodes, bacteria, fungi, and viruses) in controlling pest populations. There are three biological pest control strategies: classical biological control, conservation, and augmentation. Because Rhynchophorus ferrugineus (red palm weevil, RPW) and Paysandisia archon (palm borer moth, PBM) are invasive species in a large area, it could be hypothesized that the only feasible and suitable biocontrol method is classical biological control, defined as “the intentional introduction of an exotic biological control agent for permanent establishment and long-term pest control” (Eilenberg, Hajek, and Lomer 2001). Unfortunately, there are few reports on parasitoids and predators of these two palm pests in their native areas, probably because they do not cause important damage in those areas. RPW eggs, larvae, and adults are preys of the black earwig Chelisoches morio (Fabr.) (Dermaptera: Chelisochidae). The common blackbird (Turdus merula L.), the common kestrel (Falco tinnunculus L.), and the common magpie (Pica pica L.) have also been described to feed on adults and larvae of PBM and RPW. In addition, some mammals, such as bats and rats, can be occasional predators of adults of both the weevil and the moth. However, the practical use of mammals, reptiles, and birds in classical biological control is limited. There is some parasitization of R. ferrugineus larvae by the large wasp Scolia erratica Smith and by the calliphorid fly Sarcophaga fuscicauda Bottcher, but again, they do not play a significant role in limiting the pest populations. Laboratory experiments performed with several strains of Trichogramma have shown this parasitoid's potential for PBM egg control. Among entomopathogenic microorganisms, the bacteria Bacillus thuringiensis (Berliner) and Pseudomonas aeruginosa (Schroeter) showed low activity against RPW larvae in laboratory assays. An unidentified species of the cytoplasmic polyhedrosis virus group has been reported to infect all stages of RPW, with laboratory infections of late instars resulting in the development of malformed adults. Natural infections of RPW by the genera Heterorhabditis and Steinernema have been occasionally recorded, but inundative release of commercial strains of Steinernema carpocapsae (Weiser) (Nematoda: Steinernematidae) produced inconsistent data. Recent studies have revealed the natural occurrence of entomopathogenic fungi in weevil and moth populations throughout the Mediterranean Basin, and the efficacy of several indigenous strains of Beauveria sp. and Metarhizium sp. against larvae of both species and adults of RPW has been ascertained under laboratory and field conditions using different approaches. (Resume d'auteur)