Underestimated impact of Red Palm Weevil introduction on iandscape biodiversity: the help of the molecular tools

Abstract

Alien species have been introduced both accidentally and intentionally. The last are and have been motivated by economic, environmental and social considerations (NOBANIS, 2010), as in the case of many palm species (Phoenix canariensis, P. dactylifera, Washingtonia filifera, W. robusta) in Sicily. These Arecaceae are important in the urban areas and they contribute to the typical Sicilian Panorama. On the other hand the accidental introduction of invasive alien species can be one a cause of the loss of native biodiversity, especially severe on islands and other isolated ecosystems. Phytophagous insects can cause biodiversity losses and may also have a strong impact on the economy of the island and on the landscape. The adverse effects of invasive alien insects are illustrated by specific examples from Sicily, including the multiple impacts of the invasive weevil Rhynchophourous ferrugineus (Manachini et al., 2012), native to Malesia but quickly spread throughout Europe where it preferably attacks P. canariensis. It is noted that RPW aggressively spreads from P. canariensis to other not native hosts (eg. Washingtonia spp., Sabal spp.) and to native palm Chamaerops humilis L. (Arecaceae). This poses a threat to natural plant communities, biodiversity and landscape (Manachini et al., 2012). There is evidence that in a new territory the invasive species populations for some time exist in a kind of latent state, during which due to repeated invasions and hybridization as well as the mutations the level of genetic diversity is restored, which is usually reduced due to genetic processes occurring in the course of invasion (genetic drift, bottleneck, founder effect) (McRay & Latta 2002). Moreover there was reported that change in the host preferences could lead or due to genetic differences and to a formation of different species or sub-species (Drès & Mallet, 2002). It is known that for weevil species, host choice did not only depend on host phenology, but also on other physical and chemical factor, and this could be link to genetic differentiation. To make a clear assignment of weevil species or race independently of possible morphological plasticity, we decided to use molecular markers. These tools have the additional advantage of being applicable to both immature and adult individuals. We used a mitochondrial and a nuclear marker, because comparison between the two can detect also hybridization. The mitochondrial marker was the COI gene, which encodes for the first subunit of the cytochrome oxidase, one of the most frequently sequenced genes used in insect phylogeny (Caterino et al., 2000), already identified by the authors for RPW. Mitochondrial and nuclear sequences data showed that RPWs collected in different areas can be recognised at all different instars by molecular analysis and that all weevils came from different hosts belong to the same specie, and closed population, this lead to recognised the potential risk of extend its attack more on C. humilis. Biological data on the RPW form different infested palms confirm this potential danger that can lead to a change in the native biodiversity sustained by the presence of C. humilis.