The lesser of two weevils: molecular-genetics of pest palm weevil populations confirm Rhynchophorus vulneratus (Panzer 1798) as a valid species distinct from R. ferrugineus (Olivier 1790), and reveal the global extent of both

Abstract

The red palm weevil (RPW) is a major pest of palms. It is native to southeast Asia and Melanesia, but in recent decades has vastly expanded its range as the result of multiple accidental anthropogenic introductions into the Middle East, Mediterranean Basin, Caribbean, and U.S.A. Currently regarded as a single species, Rhynchophorus ferrugineus (Olivier), RPW displays remarkable color variation across its range, and consequently has a taxonomic history littered with new species descriptions and synonymization. We compared DNA sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene from RPW populations throughout the native and invaded ranges, to investigate the specific status and invasion history of this serious economic pest, and to identify possible common routes of entry. Analyses of COI haplotype data provide conclusive support, corroborated by sequences of additional nuclear gene regions, for the existence of at least two predominantly allopatric species. The true R. ferrugineus is native only to the northern and western parts of continental southeast Asia, Sri Lanka and the Philippines, and is responsible for almost all invasive populations worldwide. In contrast, the second species, which is currently synonymized under R. ferrugineus and should be resurrected under the name R. vulneratus (Panzer), has a more southern distribution across Indonesia, and is responsible for only one invasive population; that in California, U.S.A. The distribution of COI haplotypes is used to discuss the possible existence of further cryptic species, sources and routes of entry of different invasive populations, and the implications of our findings for current control methods.

Figure 1. The extremes of color polymorphism in adult specimens currently classified as red palm weevil, Rhynchophorus ferrugineus.

Molecular genetic data presented herein confirms that these specimens in fact represent at least two species, R. ferrugineus and R. vulneratus.

Figure 2. Strong phylogenetic and phylogeographic signal revealed by the genealogical relationships of COI haplotypes inferred using neighbour-joining (NJ) and maximum likelihood (ML) methods.

Haplotypes fell into three lineages (L1-L3) and are numbered according to their position (top to bottom) within each lineage in the NJ tree (those in L1 follow on from the eight haplotypes of El-Mergawy et al. [2011c]). Bootstrap consensus NJ tree was computed using Kimura 2-parameter distances and 1000 replicates in MEGA 5.05. Branches with <50% support have been collapsed and in all other cases, bootstrap support is shown next to the branch. ML tree constructed in PhyML. Branch support was assessed using the approximate likelihood-ratio test (SH-Like) and branches with a probability below 0.5 have been collapsed. Support for major branches is shown next to the branch. Abbreviations (where used): TH=Thailand, MY=Malaysia, UAE=United Arab Emirates, KSA=Kingdom of Saudi Arabia, Medit.=Countries of the Mediterranean basin (including Egypt, but excluding Syria).

Figure 3. Overlapping distributions of three estimates of pronotal shape in red palm weevils from lineages L1 and L3.

Figure 4. Global distribution of R. ferrugineus and R. vulneratus.

Figure 5. Color polymorphism in R. ferrugineus specimens captured in a single night in pheromone traps deployed in a commercial coconut plantation in Oct. 2011, Laguna Province, Luzon, the Philippines.