Ipini

Abstract: Ips bark beetles (Curculionidae: Scolytinae) occur in conifer forests of North America (23 species) and Eurasia (14 species). Larvae and adults feed under the bark of pine or spruce and are less common in fir, cedar, and larch. Most beetles are decomposers of dead and dying trees but some species will kill healthy trees. As males bore into the tree, they produce pheromones, which attract conspecifics and in some cases deter heterospecifics. These phenomena inspired much research concerning beetle population dynamics and the molecular basis of pheromone production. Diversification of conifers over ≈ 20 million years influenced Ips diversity while Pleistocene glaciation influenced intraspecific genetic diversity. For over 200 years, taxonomic study of Ips occurred without an explicit species concept. However, post-modern synthesis systematic studies discovered cryptic species via breeding experiments, and monophyly of Ips via molecular phylogenetics. Timing of species divergence and evolutionary ecology were inferred from these phylogenies. In addition, diagnoses, in comparison to related and allopatric species, are given for all Ips species.

Abstract: In Central Europe seven Ips species are characterized by differences in morphology, structure of galleries, host specificity and aggressiveness. These species were analysed by allozyme markers and by sequencing 567 bp of the mitochondrial cytochrome oxidase I gene, in order to define their phylogenetic relationships. Orthotomicus erosus and Tomicus minor were taken as outgroup species. The data revealed high inter-specific and low intra-specific sequence divergence. Plotting the observed sequence divergence caused by transversions (Tv) and transitions (Ts) and the level of saturation for Ts and Tv of each codon position showed that the third positions were highly saturated by multiple substitutions. Maximum parsimony analysis produced two groups: (1) I. typographus, I. cembrae, I. amitinus, I. duplicatus and I. acuminatus; (2) I. mannsfeldi, I. sexdentatus and the two outgroups. In all analyses the species of the first cluster were put together and I. typographus and I. cembrae, and I. mannsfeldi and O. erosus emerged as sister pairs. The data do not support a common ancestor for the seven European Ips species. The eight-spined bark beetles (except I. mannsfeldi) and I. acuminatus formed a monophyletic group. The close relationship of I. mannsfeldi and O. erosus supports the latter belonging to the genus Ips as proposed by Wood (1982) and Escherich (1923). However, more genetic markers and more species of the genera Orthotomicus and Pityokteines have to be analysed to resolve the phylogenetic positions of I. sexdentatus and I. mannsfeldi within the tribe Ipini.

Abstract: Bark beetles of the subfamily Scolytinae employ aggregation pheromones to attract conspecifics to their host trees (predominantly conifers) for the purposes of mating and resource exploitation. These aggregation pheromones consist of blends of chemical components whose composition is typically species specific. Across tribes and genera within the Scolytinae there are clear phylogenetic patterns in these compounds. However, within these clades differences in pheromone composition may be as great between closely related species as between more distantly related species. Here we review our understanding of the evolution of aggregation pheromone diversity in this group including discussion of the mode of evolution, and the ecological, genetic and biosynthetic mechanisms that may explain this diversity. We also collate information from the literature on the aggregation pheromone composition for 65 species of bark beetles across 17 genera, including intraspecific variation. We relate this information to evolutionary relationships to ascertain the extent to which pheromone composition reflects phylogeny. As with previous studies, we show that the mode of pheromone evolution can be characterised by substantial saltational changes in chemical composition at speciation events. We also demonstrate that some individual components are strongly phylogenetically conserved within clades, while others are phylogenetically labile. This suggests that differences in aggregation pheromone composition may arise through a combination of relatively rapid ‘switching on and switching off’ of certain compounds (eg, ipsdienol and ipsenol in the Ipini), while other compounds remain more stable once their use has evolved. We discuss these findings in the context of recent theory on the evolution of species-specific attractive pheromones.

Abstract: Micracidini (Coleoptera: Curculionidae: Scolytinae) is an unusual tribe of mainly bigynous bark beetles found in dry forests and scrublands in Afrotropical and Neotropical regions. Their phylogenetic relationship to other bark beetle groups is poorly known with few clues from external morphology. Hence, a phylogenetic analysis of five genes (COI, EF-1a, 28S, CAD, ArgK) and morphological (internal and external) data was conducted to test potential sister group relationships, including 56 outgroup genera in 22 tribes, and 18 species in 10 genera of Micracidini. Cactopinus Schwarz – a genus with many cactus feeding species – was nested within a clade of all Neotropical and Nearctic genera. The New World was colonised by an Afrotropical ancestor about 75–85 million years ago, where cactus feeding in Cactopinus evolved much later. All analyses indicated a paraphyletic clade of Afrotropical micracidines, strongly supporting inclusion of the Ipini genus Dendrochilus Schedl in Afromicracis Schedl. Hypoborini appear to be one of the more plausible sistergroup candidates to Micracidini, and revealed morphological similarity in protibial and proventricular characters. Most phylogenetic results were supported independently by morphological and molecular data and therefore document the power of thorough examination of morphological characters analysed properly in a phylogenetic context.