Weevil

Abstract: An overview is presented of the progress made on the taxonomy, classification and phylogeny of weevils in the 250 years since the first taxonomic descriptions of weevils by Carolus Linnaeus. The number of described weevils species is calculated to be about 62 000 and the likely total number of existing species 220 000, indicating that we have described just over a quarter of the diversity of this important group of beetles and that, at current rates of discovery and description, it will take another 650 years or so to describe the rest. Within the framework of the current concept of weevil phylogeny, a brief account is given of the seven main weevil lineages (families), and of the subfamilies of the largest of them, the Curculionidae, summarising their diversity, distribution and biology and identifying the major classificatory problems remaining in each. In conjunction with the phylogenetic hypothesis of weevil relationships and their fossil record, which is briefly summarised, the evolutionary history of weevils is mapped as a sequence of key evolutionary innovations that together have led to the phenomenal diversification and success of weevils.

Abstract: The extraordinary diversity of herbivorous beetles is usually attributed to coevolution with angiosperms. However, the degree and nature of contemporaneity in beetle and angiosperm diversification remain unclear. Here we present a large-scale molecular phylogeny for weevils (herbivorous beetles in the superfamily Curculionoidea), one of the most diverse lineages of insects, based on ≈8 kilobases of DNA sequence data from a worldwide sample including all families and subfamilies. Estimated divergence times derived from the combined molecular and fossil data indicate diversification into most families occurred on gymnosperms in the Jurassic, beginning ≈166 Ma. Subsequent colonization of early crown-group angiosperms occurred during the Early Cretaceous, but this alone evidently did not lead to an immediate and major diversification event in weevils. Comparative trends in weevil diversification and angiosperm dominance reveal that massive diversification began in the mid-Cretaceous (ca. 112.0 to 93.5 Ma), when angiosperms first rose to widespread floristic dominance. These and other evidence suggest a deep and complex history of coevolution between weevils and angiosperms, including codiversification, resource tracking, and sequential evolution.

Abstract: Cell physiology in the weevil Sitophilus oryzae is coordinated by three integrated genomes: nuclear, mitochondrial, and the “S. oryzae principal endosymbiont” (SOPE). SOPE, a cytoplasmic bacterium (2 × 103 bacteria per specialized bacteriocyte cell and 3 × 106 bacteria per weevil) that belongs to the proteobacteria γ3-subgroup, is present in all weevils studied. We discovered a fourth prokaryotic genome in somatic and germ tissues of 57% of weevil strains of three species, S. oryzae, Sitophilus zeamais, and Sitophilus granarius, distributed worldwide. We assigned this Gram-negative prokaryote to the Wolbachia group (α-proteobacteria), on the basis of 16S rDNA sequence and fluorescence in situ DNA–RNA hybridization (FISH). Both bacteria, SOPE and Wolbachia, were selectively eliminated by combined heat and antibiotic treatments. Study of bacteria involvement in this insect’s genetics and physiology revealed that SOPE, which induces the specific differentiation of the bacteriocytes, increases mitochondrial oxidative phosphorylation through the supply of pantothenic acid and riboflavin. Elimination of this γ3-proteobacterium impairs many physiological traits. By contrast, neither the presence nor the absence of Wolbachia significantly affects the weevil’s physiology. Wolbachia, disseminated throughout the body cells, is in particularly high density in the germ cells, where it causes nucleocytoplasmic incompatibility. The coexistence of two distinct types of intracellular proteobacteria at different levels of symbiont integration in insects illustrates the genetic complexity of animal tissue. Furthermore, evolutionary timing can be inferred: first nucleocytoplasm, then mitochondria, then SOPE, and finally Wolbachia. Symbiogenesis, the genetic integration of long-term associated members of different species, in the weevil appears to be a mechanism of speciation (with Wolbachia) and provides a means for animals to acquire new genes that permit better adaptation to the environment (with SOPE).

Abstract: The red palm weevil, Rhynchophorus ferrugineus, invaded the Gulf states in the mid-1980s, where it is now causing severe damage to date palms. This polyphagous insect is widely found in southern Asia and Melanesia where it is a well-known problem for the damage it causes to coconuts grown in plantations. In this region, the weevil is sympatric with four other Asian Rhynchophorusspecies but the taxonomic status of some of these is unclear and some may be conspecific with the red palm weevil. Current tactics to manage the weevil in the Gulf and Asia are largely based on insecticide applications although there are now deep concerns about environmental pollution. Much research has been conducted on other techniques, notably pheromone traps. However, there is now a strong emphasis on the development of integrated pest management (IPM) based on pheromone traps and biological control rather than insecticides. Here we review the biogeography, basis of population outbreaks and current management tactics for the red palm weevil and related species, and then assess the potential of biological control to underpin the development of an IPM programme for it.