Evolution, types, and distribution of flight control devices on wings and elytra in bark beetles

Gaining the ability to fly actively was a ground-breaking moment in insect evolution, providing an unprecedented advantage over other arthropods. Nevertheless, active flight was a costly innovation, requiring the development of wings and flight muscles, the provision of sufficient energetic resources, and a complex flight control system. Although wings, flight muscles, and the energetic budget of insects have been intensively studied in the last decades, almost nothing is known regarding the flight-control devices of many crucial insect groups, especially beetles (Coleoptera). Here, we conducted a phylogenetic-informed analysis of flight-related mechanosensors in 28 species of bark beetles (Curculionidae: Scolytinae, Platypodinae), an economically and ecologically important group of insects characterized by striking differences in dispersal abilities. The results indicated that beetle flight apparatus is equipped with different functional types of mechanosensors, including strain- and flow-encoding sensilla. We found a strong effect of allometry on the number of mechanosensors, while no effect of relative wing size (a proxy of flight investment) was identified. Our study constitutes the first step to understanding the drivers and constraints of the evolution of flight-control devices in Coleoptera, including bark beetles. More research, including a quantitative neuroanatomical analysis of beetle wings, should be conducted in the future.

Drift drives the evolution of chromosome number I: The impact of trait transitions on genome evolution in Coleoptera

Chromosomal mutations such as fusions and fissions are often thought to be deleterious, especially in heterozygotes (underdominant), and consequently are unlikely to become fixed. Yet, many models of chromosomal speciation ascribe an important role to chromosomal mutations. When the effective population size (Ne) is small, the efficacy of selection is weakened, and the likelihood of fixing underdominant mutations by genetic drift is greater. Thus, it is possible that ecological and phenotypic transitions that modulate Ne facilitate the fixation of chromosome changes, increasing the rate of karyotype evolution. We synthesize all available chromosome number data in Coleoptera and estimate the impact of traits expected to change Ne on the rate of karyotype evolution in the family Carabidae and 12 disparate clades from across Coleoptera. Our analysis indicates that in Carabidae, wingless clades have faster rates of chromosome number increase. Additionally, our analysis indicates clades exhibiting multiple traits expected to reduce Ne, including strict inbreeding, oligophagy, winglessness, and island endemism, have high rates of karyotype evolution. Our results suggest that chromosome number changes are likely fixed by genetic drift despite an initial fitness cost and that chromosomal speciation models may be important to consider in clades with very small Ne.

Two sympatric lineages of Australian Cnestus solidus share Ambrosiella symbionts but not Wolbachia

Sympatric lineages of inbreeding species provide an excellent opportunity to investigate species divergence patterns and processes. Many ambrosia beetle lineages (Curculionidae: Scolytinae) reproduce by predominant inbreeding through sib mating in nests excavated in woody plant parts wherein they cultivate symbiotic ambrosia fungi as their sole source of nutrition. The Xyleborini ambrosia beetle species Cnestus solidus and Cnestus pseudosolidus are sympatrically distributed across eastern Australia and have overlapping morphological variation. Using multilocus sequencing analysis of individuals collected from 19 sites spanning their sympatric distribution, we assessed their phylogenetic relationships, taxonomic status and microbial symbionts. We found no genetic differentiation between individuals morphologically identified as C. solidus and C. pseudosolidus confirming previous suggestions that C. pseudosolidus is synonymous to C. solidus. However, within C. solidus we unexpectedly discovered the sympatric coexistence of two morphologically indistinguishable but genetically distinct lineages with small nuclear yet large mitochondrial divergence. At all sites except one, individuals of both lineages carried the same primary fungal symbiont, a new Ambrosiella species, indicating that fungal symbiont differentiation may not be involved in lineage divergence. One strain of the maternally inherited bacterial endosymbiont Wolbachia was found at high prevalence in individuals of the more common lineage but not in the other, suggesting that it may influence host fitness. Our data suggest that the two Australian Cnestus lineages diverged allopatrically, and one lineage then acquired Wolbachia. Predominant inbreeding and Wolbachia infection may have reinforced reproductive barriers between these two lineages after their secondary contact contributing to their current sympatric distribution.

Fidelity or love the one you're with? Biotic complexity and tradeoffs can drive strategy and specificity in beetle-fungus by-product mutualisms

By-product mutualisms are ubiquitous yet seldom considered in models of mutualism. Most models represent conditional mutualisms that shift between mutualism and antagonism in response to shifts in costs and benefits resulting from changes in environmental quality. However, in by-product mutualisms, benefits arise as a part of normal life processes that may be costly to produce but incur little-to-no additional costs in response to the interaction. Without costs associated with the interaction, they do not have antagonistic alternate states. Here, we present a conceptual model that differs from traditional conditional models in three ways: (1) partners exchange by-product benefits, (2) interactions do not have alternate antagonistic states, and (3) tradeoffs are allowed among factors that influence environmental quality (rather than all factors that contribute to environmental quality being combined into a single gradient ranging from high to low). We applied this model to bark and ambrosia beetles (Curculionidae: Scolytinae), a diverse group that associates with fungi and that has repeatedly developed two distinct pathways to by-product mutualism. We used independent axes for each major factor influencing environmental quality in these systems, including those that exhibit tradeoffs (tree defense and nutritional quality). For these symbioses, tradeoffs in these two factors are key to which mutualism pathway is taken.

The tribal placement of Urocorthylus Petrov, Mandelshtam & Beaver, with a description of the male of U. hirtellus Petrov et al., and notes on its biology (Coleoptera: Curculionidae: Scolytinae)

We show, using molecular data, that the enigmatic genus Urocorthylus Petrov, Mandelshtam & Beaver from Southeast Asia belongs in the scolytine tribe, Dryocoetini, and not in the almost wholly American tribe Corthylini, where it was originally placed. The male of Urocorthylus hirtellus Petrov, Mandelshtam & Beaver is described and figured for the first time, and new records from China are presented. Urocorthylus hirtellus is a bark beetle, and not an ambrosia beetle as originally hypothesised. Keys are provided to the genus within the Dryocoetini, and to the two species included in the genus.

Genome analysis and genomic comparison of a fungal cultivar of the nonsocial weevil Euops chinensis reveals its plant decomposition and protective roles in fungus-farming mutualism

Fungus-farming mutualisms are models for studying co-evolutionary among species. Compared to well-documented fungus-farming in social insects, the molecular aspects of fungus-farming mutualisms in nonsocial insects have been poorly explored. Euops chinensis is a solitary leaf-rolling weevil feeding on Japanese knotweed (Fallopia japonica). This pest has evolved a special proto-farming bipartite mutualism with the fungus Penicillium herquei, which provide nutrition and defensive protection for the E. chinensis larvae. Here, the genome of P. herquei was sequenced, and the structure and specific gene categories in the P. herquei genome were then comprehensively compared with the other two well-studied Penicillium species (P. decumbens and P. chrysogenum). The assembled P. herquei genome had a 40.25  Mb genome size with 46.7% GC content. A diverse set of genes associating with carbohydrate-active enzymes, cellulose and hemicellulose degradation, transporter, and terpenoid biosynthesis were detected in the P. herquei genome. Comparative genomics demonstrate that the three Penicillium species show similar metabolic and enzymatic potential, however, P. herquei has more genes associated with plant biomass degradation and defense but less genes associating with virulence pathogenicity. Our results provide molecular evidence for plant substrate breakdown and protective roles of P. herquei in E. chinensis mutualistic system. Large metabolic potential shared by Penicillium species at the genus level may explain why some Penicillium species are recruited by the Euops weevils as crop fungi.

Ecuadorian Coptoborus beetles harbor Fusarium and Graphium fungi previously associated with Euwallacea ambrosia beetles

Ambrosia beetles from the scolytine tribe Xyleborini (Curculionidae) are important to the decomposition of woody plant material on every continent except Antarctica. These insects farm fungi on the walls of tunnels they build inside recently dead trees and rely on the fungi for nutrition during all stages of their lives. Such ambrosia fungi rely on the beetles to provide appropriate substrates and environmental conditions for growth. A small minority of xyleborine ambrosia beetle-fungal partnerships cause significant damage to healthy trees. The xyleborine beetle Coptoborus ochromactonus vectors a Fusarium (Hypocreales) fungus that is lethal to balsa (Ochroma pyramidale (Malvaceae)) trees in Ecuador. Although this pathogenic fungus and its associated beetle are not known to be established in the United States, several other non-native ambrosia beetle species are vectors of destructive plant diseases in this country. This fact and the acceleration of trade between South America and the United States demonstrate the importance of understanding fungal plant pathogens before they escape their native ranges. Here we identify the fungi accompanying Coptoborus ambrosia beetles collected in Ecuador. Classification based ribosomal internal transcribed spacer 1 (ITS) sequences revealed the most prevalent fungi associated with Coptoborus are Fusarium sp. and Graphium sp. (Microascales: Microascaceae), which have been confirmed as ambrosia fungi for xyleborine ambrosia beetles, and Clonostsachys sp. (Hypocreales), which is a diverse genus found abundantly in soils and associated with plants. Phylogenetic analyses of the Fusarium strains based on ITS, translation elongation factor (EF1-α), and two subunits of the DNA-directed RNA polymerase II (RPB1 and RPB2) identified them as Fusarium sp. AF-9 in the Ambrosia Fusarium Clade (AFC). This Fusarium species was previously associated with a few xyleborine ambrosia beetles, most notably the species complex Euwallacea fornicatus (Eichhoff 1868) (Curculionidae: Scolytinae: Xyleborini). Examination of ITS and EF1-α sequences showed a close affinity between the Graphium isolated from Coptoborus spp. and other xyleborine-associated Graphium as well as the soil fungus Graphium basitruncatum. This characterization of ambrosia fungi through DNA sequencing confirms the identity of a putative plant pathogen spread by Coptoborus beetles and expands the documented range of Fusarium and Graphium ambrosia fungi.

Origin and evolution of fungus farming in wood-boring Coleoptera - a palaeontological perspective

Insect-fungus mutualism is one of the better-studied symbiotic interactions in nature. Ambrosia fungi are an ecological assemblage of unrelated fungi that are cultivated by ambrosia beetles in their galleries as obligate food for larvae. Despite recently increased research interest, it remains unclear which ecological factors facilitated the origin of fungus farming, and how it transformed into a symbiotic relationship with obligate dependency. It is clear from phylogenetic analyses that this symbiosis evolved independently many times in several beetle and fungus lineages. However, there is a mismatch between palaeontological and phylogenetic data. Herein we review, for the first time, the ambrosia system from a palaeontological perspective. Although largely ignored, families such as Lymexylidae and Bostrichidae should be included in the list of ambrosia beetles because some of their species cultivate ambrosia fungi. The estimated origin for some groups of ambrosia fungi during the Cretaceous concurs with a known high diversity of Lymexylidae and Bostrichidae at that time. Although potentially older, the greatest radiation of various ambrosia beetle lineages occurred in the weevil subfamilies Scolytinae and Platypodinae during the Eocene. In this review we explore the evolutionary relationship between ambrosia beetles, fungi and their host trees, which is likely to have persisted for longer than previously supposed.

A revision of the Neotropical genus Coptoborus Hopkins (Coleoptera, Curculionidae, Scolytinae, Xyleborini)

The Neotropical xyleborine ambrosia beetle genus Coptoborus Hopkins is reviewed. The following 40 Coptoborus species are described: C. amplissimus sp. nov. (Peru), C. asperatus sp. nov. (Ecuador), C. barbicauda sp. nov. (French Guiana), C. bettysmithae sp. nov. (Ecuador), C. brevicauda sp. nov. (Ecuador), C. brigman sp. nov. (Ecuador), C. busoror sp. nov. (Ecuador), C. capillisoror sp. nov. (Brazil), C. chica sp. nov. (Suriname), C. crassisororcula sp. nov. (Peru), C. doliolum sp. nov. (Ecuador), C. erwini sp. nov. (Ecuador), C. furiosa sp. nov. (Ecuador), C. galacatosae sp. nov. (Ecuador), C. hansen sp. nov. (Brazil), C. incomptus sp. nov. (Peru), C. janeway sp. nov. (Peru), C. katniss sp. nov. (Ecuador), C. leeloo sp. nov. (Ecuador), C. leia sp. nov. (Ecuador, Suriname), C. leporinus sp. nov. (Peru), C. martinezae sp. nov. (Ecuador), C. murinus sp. nov. (Ecuador), C. newt sp. nov. (Peru), C. osbornae sp. nov. (Ecuador), C. panosus sp. nov. (French Guiana), C. papillicauda sp. nov. (Suriname), C. pilisoror sp. nov. (Ecuador), C. ripley sp. nov. (Ecuador), C. sagitticauda sp. nov. (Guyana), C. sarahconnor sp. nov. (Brazil), C. scully sp. nov. (Ecuador), C. sicula sp. nov. (Ecuador), C. sororcula sp. nov. (Peru), C. starbuck sp. nov. (Ecuador), C. trinity sp. nov. (Brazil), C. uhura sp. nov. (Peru), C. vasquez sp. nov. (Panama), C. vrataski sp. nov. (Brazil), and C. yar sp. nov. (Ecuador). Seventeen new combinations are given: Coptoborus amazonicus (Petrov, 2020) comb. nov., C. atlanticus (Bright & Torres, 2006) comb. nov., C. bellus Bright & Torres, 2006 comb. nov., C. coartatus (Sampson, 1921) comb. nov., C. crinitulus (Wood, 1974) comb. nov., C. exilis (Schedl, 1934) comb. nov., C. incultus (Wood, 1975) comb. nov., C. magnus (Petrov, 2020) comb. nov., C. micarius (Wood, 1974) comb. nov., C. obtusicornis (Schedl, 1976) comb. nov., C. paurus (Wood, 2007) comb. nov., C. pristis (Wood, 1974) comb. nov., C. pseudotenuis (Schedl, 1936) comb. nov., C. puertoricensis (Bright & Torres, 2006) comb. nov., C. ricini (Eggers, 1932) comb. nov., C. semicostatus (Schedl, 1948) comb. nov., C. tristiculus (Wood, 1975) comb. nov., and C. villosulus (Blandford, 1898) comb. nov. Two new synonyms are proposed: Coptoborus Hopkins, 1915 (= Theoborus Hopkins, 1915 syn. nov.) and Coptoborus villosulus (Blandford, 1898) (= Theoborus theobromae Hopkins, 1915 syn. nov.). Xyleborus neosphenos Schedl, 1976 comb. res. is removed from Coptoborus. The revised genus now contains 77 species and a key to their identification is provided.

Ecological and biogeographic drivers of biodiversity cannot be resolved using clade age-richness data

Estimates of evolutionary diversification rates - speciation and extinction - have been used extensively to explain global biodiversity patterns. Many studies have analyzed diversification rates derived from just two pieces of information: a clade's age and its extant species richness. This "age-richness rate" (ARR) estimator provides a convenient shortcut for comparative studies, but makes strong assumptions about the dynamics of species richness through time. Here we demonstrate that use of the ARR estimator in comparative studies is problematic on both theoretical and empirical grounds. We prove mathematically that ARR estimates are non-identifiable: there is no information in the data for a single clade that can distinguish a process with positive net diversification from one where net diversification is zero. Using paleontological time series, we demonstrate that the ARR estimator has no predictive ability for real datasets. These pathologies arise because the ARR inference procedure yields "point estimates" that have been computed under a saturated statistical model with zero degrees of freedom. Although ARR estimates remain useful in some contexts, they should be avoided for comparative studies of diversification and species richness.

Patterns of host tree use within a lineage of saproxlic snout-less weevils (Coleoptera: Curculionidae: Scolytinae: Scolytini)

The influence of plants in the diversification of herbivorous insects, specifically those that utilize moribund and dead hosts, is little explored. Host shifts are expected because the effectiveness of toxic secondary chemicals is lessened by decay of dead plants. Feeding on dead plants also releases herbivorous insect lineages from diversifying within a particular plant lineage. Thus, phylogenetic constraints on the herbivorous insect lineage imposed by the host plants are diminished and repeated patterns of species diversification in an association with unrelated host trees is hypothesized (i.e., taxon cycle). Scolytini, a diverse weevil tribe, specialize on many different dead and moribund plant taxa as a source of food. These species and their hosts offer an opportunity to examine the association between dead host plants and the extent of phylogenetic constraints. A phylogeny of the Scolytini was reconstructed with likelihood and Bayesian analyses of DNA sequence data from nuclear (28S, CAD, ArgK) and mitochondrial (COI) genes. Ancestral host usage and geography was reconstructed using likelihood criteria and conservation of host use was tested. Results supported a monophyletic Scolytini, Ceratolepis, Loganius, and a paraphyletic Scolytus, Camptocerus and Cnemonyx. Diversification of the Scolytini generally occurred well after their host taxa diversified and suggests a sequential evolution of host use. In this scenario the beetle imposes little selection pressure on the tree but the tree provides a platform for beetle evolution. Major changes in host tree use occurred during periods of global cooling associated with changes in beetle biogeography. Diversification of beetles occurred on common and widespread hosts and there was likely a single origination of conifer-feeding from angiosperm-feeding species during the early Pliocene and a radiation of beetle species from the Palearctic to the Nearctic. Overall, the observed patterns of Scolytini host use are conserved and are similar to those expected in a taxon pulse diversification. That is, after a host switch to an unrelated tree, the beetles diversify within the host plant lineage. The need to locate an ephemeral food resource, i.e., a dying tree, likely maintains host specificity once a host shift occurs. These findings suggest that characteristics of dead and moribund host plants (e.g. secondary chemicals) influence the diversification of these saproxlic weevils despite the reduction of selection pressures.

A monograph of the Xyleborini (Coleoptera, Curculionidae, Scolytinae) of the Indochinese Peninsula (except Malaysia) and China

The Southeast Asian xyleborine ambrosia beetle fauna is reviewed for the first time. Thirty-four genera and 315 species are reviewed, illustrated, and keyed to genera and species. Sixty-three new species are described: Amasa cycloxyster sp. nov., Amasa galeoderma sp. nov., Amasa gibbosa sp. nov., Amasa lini sp. nov., Amasa tropidacron sp. nov., Amasa youlii sp. nov., Ambrosiophilus caliginestris sp. nov., Ambrosiophilus indicus sp. nov., Ambrosiophilus lannaensis sp. nov., Ambrosiophilus papilliferus sp. nov., Ambrosiophilus wantaneeae sp. nov., Anisandrus achaete sp. nov., Anisandrus auco sp. nov., Anisandrus auratipilus sp. nov., Anisandrus congruens sp. nov., Anisandrus cryphaloides sp. nov., Anisandrus feronia sp. nov., Anisandrus hera sp. nov., Anisandrus paragogus sp. nov., Anisandrus sinivali sp. nov., Anisandrus venustus sp. nov., Anisandrus xuannu sp. nov., Arixyleborus crassior sp. nov., Arixyleborus phiaoacensis sp. nov., Arixyleborus setosus sp. nov., Arixyleborus silvanus sp. nov., Arixyleborus sittichayai sp. nov., Arixyleborus titanus sp. nov., Coptodryas amydra sp. nov., Coptodryas carinata sp. nov., Coptodryas inornata sp. nov., Cyclorhipidion amasoides sp. nov., Cyclorhipidion amputatum sp. nov., Cyclorhipidion denticauda sp. nov., Cyclorhipidion muticum sp. nov., Cyclorhipidion obesulum sp. nov., Cyclorhipidion petrosum sp. nov., Cyclorhipidion truncaudinum sp. nov., Cyclorhipidion xeniolum sp. nov., Euwallacea geminus sp. nov., Euwallacea neptis sp. nov., Euwallacea subalpinus sp. nov., Euwallacea testudinatus sp. nov., Heteroborips fastigatus sp. nov., Heteroborips indicus sp. nov., Microperus latesalebrinus sp. nov., Microperus minax sp. nov., Microperus sagmatus sp. nov., Streptocranus petilus sp. nov., Truncaudum bullatum sp. nov., Xyleborinus cuneatus sp. nov., Xyleborinus disgregus sp. nov., Xyleborinus echinopterus sp. nov., Xyleborinus ephialtodes sp. nov., Xyleborinus huifenyinae sp. nov., Xyleborinus jianghuansuni sp. nov., Xyleborinus thaiphami sp. nov., Xyleborinus tritus sp. nov., Xyleborus opacus sp. nov., Xyleborus sunisae sp. nov., Xyleborus yunnanensis sp. nov., Xylosandrus bellinsulanus sp. nov., Xylosandrus spinifer sp. nov.. Thirteen new combinations are given: Ambrosiophilus consimilis (Eggers) comb. nov., Anisandrus carinensis (Eggers) comb. nov., Anisandrus cristatus (Hagedorn) comb. nov., Anisandrus klapperichi (Schedl) comb. nov., Anisandrus percristatus (Eggers) comb. nov., Arixyleborus resecans (Eggers) comb. nov., Cyclorhipidion armiger (Schedl) comb. nov., Debus quadrispinus (Motschulsky) comb. nov., Heteroborips tristis (Eggers) comb. nov., Leptoxyleborus machili (Niisima) comb. nov., Microperus cruralis (Schedl) comb. nov., Planiculus shiva (Maiti & Saha) comb. nov., Xylosandrus formosae (Wood) comb. nov. Twenty-four new synonyms are proposed: Ambrosiophilus osumiensis (Murayama, 1934) (= Xyleborus nodulosus Eggers, 1941 syn. nov.); Ambrosiophilus subnepotulus (Eggers, 1930) (= Xyleborus cristatuloides Schedl, 1971 syn. nov.); Ambrosiophilus sulcatus (Eggers, 1930) (= Xyleborus sinensis Eggers, 1941 syn. nov.; = Xyleborus sulcatulus Eggers, 1939 syn. nov.); Anisandrus hirtus (Hagedorn, 1904) (= Xyleborus hirtipes Schedl, 1969 syn. nov.); Cnestus protensus (Eggers, 1930) (= Cnestus rostratus Schedl, 1977 syn. nov.); Cyclorhipidion bodoanum (Reitter, 1913) (= Xyleborus misatoensis Nobuchi, 1981 syn. nov.); Cyclorhipidion distinguendum (Eggers, 1930) (= Xyleborus fukiensis Eggers, 1941 syn. nov.; = Xyleborus ganshoensis Murayama, 1952 syn. nov.); Cyclorhipidion inarmatum (Eggers, 1923) (= Xyleborus vagans Schedl, 1977 syn. nov.); Debus quadrispinus (Motschulsky, 1863) (= Xyleborus fallax Eichhoff, 1878 syn. nov.); Euwallacea gravelyi (Wichmann, 1914) (= Xyleborus barbatomorphus Schedl, 1951 syn. nov.); Euwallacea perbrevis (Schedl, 1951) (= Xyleborus molestulus Wood, 1975 syn. nov.; Euwallacea semirudis (Blandford, 1896) (= Xyleborus neohybridus Schedl, 1942 syn. nov.); Euwallacea sibsagaricus (Eggers, 1930) (= Xyleborus tonkinensis Schedl, 1934 syn. nov.); Euwallacea velatus (Sampson, 1913) (= Xyleborus rudis Eggers, 1930 syn. nov.); Microperus kadoyamaensis (Murayama, 1934) (= Xyleborus pubipennis Schedl, 1974 syn. nov.; =Xyleborus denseseriatus Eggers, 1941 syn. nov.); Stictodex dimidiatus (Eggers, 1927) (=Xyleborus dorsosulcatus Beeson, 1930 syn. nov.); Webbia trigintispinata Sampson, 1922 (= Webbia mucronatus Eggers, 1927 syn. nov.); Xyleborinus artestriatus (Eichhoff, 1878) (= Xyelborus angustior [sic] Eggers, 1925 syn. nov.; = Xyleborus undatus Schedl, 1974 syn. nov.); Xyleborinus exiguus (Walker, 1859) (= Xyleborus diversus Schedl, 1954 syn. nov.); Xyleborus muticus Blandford, 1894 (= Xyleborus conditus Schedl, 1971 syn. nov.; = Xyleborus lignographus Schedl, 1953 syn. nov.). Seven species are removed from synonymy and reinstated as valid species: Anisandrus cristatus (Hagedorn, 1908), Cyclorhipidion tenuigraphum (Schedl, 1953), Diuncus ciliatoformis (Schedl, 1953), Euwallacea gravelyi (Wichmann, 1914), Euwallacea semirudis (Blandford, 1896), Microperus fulvulus (Schedl, 1942), Xyleborinus subspinosus (Eggers, 1930).

Four mycangium types and four genera of ambrosia fungi suggest a complex history of fungus farming in the ambrosia beetle tribe Xyloterini

Ambrosia beetles farm fungal cultivars (ambrosia fungi) and carry propagules of the fungal mutualists in storage organs called mycangia, which occur in various body parts and vary greatly in size and complexity. The evolution of ambrosia fungi is closely tied to the evolution and development of the mycangia that carry them. The understudied ambrosia beetle tribe Xyloterini included lineages with uncharacterized ambrosia fungi and mycangia, which presented an opportunity to test whether developments of different mycangium types in a single ambrosia beetle lineage correspond with concomitant diversity in their fungal mutualists. We collected representatives of all three Xyloterini genera (Trypodendron, Indocryphalus, and Xyloterinus politus) and characterized their ambrosia fungi in pure culture and by DNA sequencing. The prothoracic mycangia of seven Trypodendron species all yielded Phialophoropsis (Microascales) ambrosia fungi, including three new species, although these relationships were not all species specific. Indocryphalus mycangia are characterized for the first time in the Asian I. pubipennis. They comprise triangular prothoracic cavities substantially smaller than those of Trypodendron and unexpectedly carry an undescribed species of Toshionella (Microascales), which are otherwise ambrosia fungi of Asian Scolytoplatypus (Scolytoplatypodini). Xyloterinus politus has two different mycangia, each with a different ambrosia fungus: Raffaelea cf. canadensis RNC5 (Ophiostomatales) in oral mycangia of both sexes and Kaarikia abrahamsonii (Sordariomycetes, genus incertae sedis with affinity for Distoseptisporaceae), a new genus and species unrelated to other known ambrosia fungi, in shallow prothoracic mycangia of females. In addition to their highly adapted mycangial mutualists, Trypodendron and X. politus harbor a surprising diversity of facultative symbionts in their galleries, including Raffaelea. A diversity of ambrosia fungi and mycangia suggest multiple ancestral cultivar captures or switches in the history of tribe Xyloterini, each associated with unique adaptations in mycangium anatomy. This further supports the theory that developments of novel mycangium types are critical events in the evolution of ambrosia beetles and their coadapted fungal mutualists.

Patterns of coevolution between ambrosia beetle mycangia and the Ceratocystidaceae, with five new fungal genera and seven new species

Ambrosia beetles farm specialised fungi in sapwood tunnels and use pocket-like organs called mycangia to carry propagules of the fungal cultivars. Ambrosia fungi selectively grow in mycangia, which is central to the symbiosis, but the history of coevolution between fungal cultivars and mycangia is poorly understood. The fungal family Ceratocystidaceae previously included three ambrosial genera (Ambrosiella, Meredithiella, and Phialophoropsis), each farmed by one of three distantly related tribes of ambrosia beetles with unique and relatively large mycangium types. Studies on the phylogenetic relationships and evolutionary histories of these three genera were expanded with the previously unstudied ambrosia fungi associated with a fourth mycangium type, that of the tribe Scolytoplatypodini. Using ITS rDNA barcoding and a concatenated dataset of six loci (28S rDNA, 18S rDNA, tef1-α, tub, mcm7, and rpl1), a comprehensive phylogeny of the family Ceratocystidaceae was developed, including Inodoromyces interjectus gen. & sp. nov., a non-ambrosial species that is closely related to the family. Three minor morphological variants of the pronotal disk mycangium of the Scolytoplatypodini were associated with ambrosia fungi in three respective clades of Ceratocystidaceae: Wolfgangiella gen. nov., Toshionella gen. nov., and Ambrosiella remansi sp. nov. Closely-related species that are not symbionts of ambrosia beetles are accommodated by Catunica adiposa gen. & comb. nov. and Solaloca norvegica gen. & comb. nov. The divergent morphology of the ambrosial genera and their phylogenetic placement among non-ambrosial genera suggest three domestication events in the Ceratocystidaceae. Estimated divergence dates for the ambrosia fungi and mycangia suggest that Scolytoplatypodini mycangia may have been the first to acquire Ceratocystidaceae symbionts and other ambrosial fungal genera emerged shortly after the evolution of new mycangium types. There is no evidence of reversion to a non-ambrosial lifestyle in the mycangial symbionts.

A selective fungal transport organ (mycangium) maintains coarse phylogenetic congruence between fungus-farming ambrosia beetles and their symbionts

Thousands of species of ambrosia beetles excavate tunnels in wood to farm fungi. They maintain associations with particular lineages of fungi, but the phylogenetic extent and mechanisms of fidelity are unknown. We test the hypothesis that selectivity of their mycangium enforces fidelity at coarse phylogenetic scales, while permitting promiscuity among closely related fungal mutualists. We confirm a single evolutionary origin of the Xylosandrus complex-a group of several xyleborine genera that farm fungi in the genus Ambrosiella. Multi-level co-phylogenetic analysis revealed frequent symbiont switching within major Ambrosiella clades, but not between clades. The loss of the mycangium in Diuncus, a genus of evolutionary cheaters, was commensurate with the loss of fidelity to fungal clades, supporting the hypothesis that the mycangium reinforces fidelity. Finally, in vivo experiments tracked symbiotic compatibility throughout the symbiotic life cycle of Xylosandrus compactus and demonstrated that closely related Ambrosiella symbionts are interchangeable, but the probability of fungal uptake in the mycangium was significantly lower in more phylogenetically distant species of symbionts. Symbiont loads in experimental subjects were similar to wild-caught beetles. We conclude that partner choice in ambrosia beetles is achieved in the mycangium, and co-phylogenetic inferences can be used to predict the likelihood of specific symbiont switches.

The Weevil Fauna Preserved in Burmese Amber—Snapshot of a Unique, Extinct Lineage (Coleoptera: Curculionoidea)

Only a few weevils have been described from Burmese amber, and although most have been misclassified, they show unusual and specialised characters unknown in extant weevils. In this paper, we present the results of a study of a much larger and more diverse selection of Burmese amber weevils. We prepared all amber blocks to maximise visibility of structures and examined these with high-magnification light microscopy as well as CT scanning (selected specimens). We redescribe most previously described taxa and describe 52 new species in 26 new genera, accompanied by photographs. We compare critical characters of these weevils with those of extant taxa and outline the effects of distortion on their preservation and interpretation. We conclude that only two weevil families are thus far represented in Burmese amber, Nemonychidae and a newly recognised family, Mesophyletidae, which appears closely related to Attelabidae but cannot be accommodated in this family. The geniculate antennae and long rostrum with exodont mandibles of most Mesophyletidae indicate that they were highly specialised phytophages of early angiosperms preserved in the amber, likely ovipositing in flowers or seeds. This weevil fauna appears to represent an extinct mid-Cretaceous ecosystem and fills a critical gap in the fossil record of weevils.

Morphological and Molecular Perspectives on the Phylogeny, Evolution, and Classification of Weevils (Coleoptera: Curculionoidea): Proceedings from the 2016 International Weevil Meeting

The 2016 International Weevil Meeting was held immediately after the International Congress of Entomology (ICE). It built on the topics and content of the 2016 ICE weevil symposium Phylogeny and Evolution of Weevils (Coleoptera: Curculionoidea): A Symposium in Honor of Dr. Guillermo "Willy” Kuschel. Beyond catalyzing research and collaboration, the meeting was intended to serve as a forum for identifying priorities and goals for those who study weevils. The meeting consisted of 46 invited and contributed lectures, discussion sessions and introductory remarks presented by 23 speakers along with eight contributed research posters. These were organized into three convened sessions, each lasting one day: (1) weevil morphology; (2) weevil fossils, biogeography and host/habitat associations; and (3) molecular phylogenetics and classification of weevils. Some of the topics covered included the 1K Weevils Project, major morphological character systems of adult and larval weevils, weevil morphological terminology, prospects for future morphological character discovery, phylogenetic analysis of morphological character data, the current status of weevil molecular phylogenetics and evolution, resources available for phylogenetic and comparative genomic studies of weevils, the weevil fossil record, weevil biogeography and evolution, weevil host plants, evolutionary development of the weevil rostrum, resources available for weevil identification and the current status of and challenges in weevil classification.

Comparative analysis of behavioural traits in insects

Comparative studies of insect behaviour based on evolutionary trees are currently blossoming, because of the increasing ease of phylogeny estimation, the availability of new trait data to analyze, and a vast and growing array of statistical techniques for exploring data and testing hypotheses. These studies address not only the selective forces and constraints on insect behaviour, which are the realm of traditional behavioural ecology, but also their ecological and evolutionary consequences. Recent studies have significantly increased our understanding of foraging behaviour, interspecific interactions, locomotion and dispersal, communication and signalling, mate choice and sexual selection, parental care and the evolution of sociality. The curating of trait data remains a significant challenge to maximize the future potential of insect comparative studies.

Identification of the Achilles heels of the laurel wilt pathogen and its beetle vector

Ambrosia beetles harbor fungal symbionts that serve as food sources for larvae and adults. These beetles lay their eggs along tunnels in xylem sapwood, which is the substrate for fungal growth. Symbiotic fungi of the genus Raffaelea found in invasive and indigenous ambrosia beetles include the highly virulent plant pathogen Raffaelea lauricola affecting members of the Lauraceae family. R. lauricola is responsible for the deaths of > 500 million trees since 2005. Infection by as few as 100 spores can kill a healthy tree within months. Our data show that R. lauricola is cold-adapted with optimal growth between 16 and 26 °C, with little to no growth at temperatures ≥ 30 °C. The fungus is halophilic and shows a dramatic decrease in growth at pH ≥ 6.8. Fungicide resistance profiling revealed sensitivity of R. lauricola to prochloraz, dichlorofluanid, most conazoles, dithiocarbamates, and zineb (zinc fungicide), whereas the related species Raffaelea arxii showed more limited fungicide sensitivity. Entomopathogenic fungi potentially useful for beetle control were generally highly resistant to most fungicides tested. Coupling pH decreased the concentration for 95% inhibition of fungal growth (IC₉₅) of the most potent R. lauricola fungicides by 3-4-fold. Use of avocado bark plug insect bioassays revealed that commercially available Beauveria bassiana can be used as a biological control agent capable of effectively killing the beetle vectors. These data provide simple and practical recommendations to specifically target R. lauricola while having minimal effects on other symbiotic and entomopathogenic fungi, the latter of which can be used to manage the beetle vectors.

Know your farmer: Ancient origins and multiple independent domestications of ambrosia beetle fungal cultivars

Bark and ambrosia beetles are highly specialized weevils (Curculionidae) that have established diverse symbioses with fungi, most often from the order Ophiostomatales (Ascomycota, Sordariomycetes). The two types of beetles are distinguished by their feeding habits and intimacy of interactions with their symbiotic fungi. The tree tissue diet of bark beetles is facilitated by fungi, while ambrosia beetles feed solely on fungi that they farm. The farming life history strategy requires domestication of a fungus, which the beetles consume as their sole food source. Ambrosia beetles in the subfamily Platypodinae originated in the mid-Cretaceous (119-88 Ma) and are the oldest known group of farming insects. However, attempts to resolve phylogenetic relationships and the timing of domestication events for fungal cultivars have been largely inconclusive. We sequenced the genomes of 12 ambrosia beetle fungal cultivars and bark beetle associates, including the devastating laurel wilt pathogen, Raffaelea lauricola, to estimate a robust phylogeny of the Ophiostomatales. We find evidence for contemporaneous diversification of the beetles and their associated fungi, followed by three independent domestication events of the ambrosia fungi genus Raffaelea. We estimate the first domestication of an Ophiostomatales fungus occurred ~86 Ma, 25 million years earlier than prior estimates and in close agreement with the estimated age of farming in the Platypodinae (96 Ma). Comparisons of the timing of fungal domestication events with the timing of beetle radiations support the hypothesis that the first large beetle radiations may have spread domesticated "ambrosia" fungi to other fungi-associated beetle groups, perhaps facilitating the evolution of new farming lineages.