Mycangia of the ambrosia beetle, Austroplatypus incompertus (Schedl) (Coleoptera: Curculionidae: Platypodinae)

Abstract  Ambrosia beetles have an obligate relationship with the ambrosia fungi that they feed on. This requires that the beetles have means to transport those fungi when they colonise new hosts. Some ambrosia beetles have special structures called mycangia to transport fungi in. This paper describes the mycangia of the ambrosia beetle Austroplatypus incompertus and illustrates how the mycangical hairs are probably used by the beetle to acquire fungal spores for transport. The mycangia and probable method of fungal acquisition of this species are compared with those of other ambrosia beetles.     

Classification of weevils as a data-driven science: leaving opinion behind

Data and explicit taxonomic ranking criteria, which minimize taxonomic change, provide a scientific approach to modern taxonomy and classification. However, traditional practices of opinion-based taxonomy (i.e., mid-20^th century evolutionary systematics), which lack explicit ranking and naming criteria, are still in practice despite phylogenetic evidence. This paper discusses a recent proposed reclassification of weevils that elevates bark and ambrosia beetles (Scolytinae and Platypodinae) to the ranks of Family. We demonstrate that the proposed reclassification 1) is not supported by an evolutionary systematic justification because the apparently unique morphology of bark and ambrosia beetles is shared with other unrelated wood-boring weevil taxa; 2) introduces obvious paraphyly in weevil classification and hence violates good practices on maintaining an economy of taxonomic change; 3) is not supported by other taxonomic naming criteria, such as time banding. We recommend the abandonment of traditional practices of an opinion-based taxonomy, especially in light of available data and resulting phylogenies.     

Relationships among wood‐boring beetles,fungi, and the decomposition of forest biomass

A prevailing paradigm in forest ecology is that wood‐boring beetles facilitate wood decay and carbon cycling, but empirical tests have yielded mixed results. We experimentally determined the effects of wood borers on fungal community assembly and wood decay within pine trunks in the southeastern United States. Pine trunks were made either beetle‐accessible or inaccessible. Fungal communities were compared using culturing and high‐throughput amplicon sequencing (HTAS) of DNA and RNA. Prior to beetle infestation, living pines had diverse fungal endophyte communities. Endophytes were displaced by beetle‐associated fungi in beetle‐accessible trees, whereas some endophytes persisted as saprotrophs in beetle‐excluded trees. Beetles increased fungal diversity several fold. Over forty taxa of Ascomycota were significantly associated with beetles, but beetles were not consistently associated with any known wood‐decaying fungi. Instead, increasing ambrosia beetle infestations caused reduced decay, consistent with previous in vitro experiments that showed beetle‐associated fungi reduce decay rates by competing with decay fungi. No effect of bark‐inhabiting beetles on decay was detected. Platypodines carried significantly more fungal taxa than scolytines. Molecular results were validated by synthetic and biological mock communities and were consistent across methodologies. RNA sequencing confirmed that beetle‐associated fungi were biologically active in the wood. Metabarcode sequencing of the LSU/28S marker recovered important fungal symbionts that were missed by ITS2, though community‐level effects were similar between markers. In contrast to the current paradigm, our results indicate ambrosia beetles introduce diverse fungal communities that do not extensively decay wood, but instead reduce decay rates by competing with wood decay fungi.     

THE EVOLUTION OF AGRICULTURE IN BEETLES (CURCULIONIDAE: SCOLYTINAE AND PLATYPODINAE)

Abstract Beetles in the weevil subfamilies Scolytinae and Platypodinae are unusual in that they burrow as adults inside trees for feeding and oviposition. Some of these beetles are known as ambrosia beetles for their obligate mutualisms with asexual fungi—known as ambrosia fungi—that are derived from plant pathogens in the ascomycete group known as the ophiostomatoid fungi. Other beetles in these subfamilies are known as bark beetles and are associated with free‐living, pathogenic ophiostomatoid fungi that facilitate beetle attack of phloem of trees with resin defenses. Using DNA sequences from six genes, including both copies of the nuclear gene encoding enolase, we performed a molecular phylogenetic study of bark and ambrosia beetles across these two subfamilies to establish the rate and direction of changes in life histories and their consequences for diversification. The ambrosia beetle habits have evolved repeatedly and are unreversed. The subfamily Platypodinae is derived from within the Scolytinae, near the tribe Scolytini. Comparison of the molecular branch lengths of ambrosia beetles and ambrosia fungi reveals a strong correlation, which a fungal molecular clock suggests spans 60 to 21 million years. Bark beetles have shifted from ancestral association with conifers to angiosperms and back again several times. Each shift to angiosperms is associated with elevated diversity, whereas the reverse shifts to conifers are associated with lowered diversity. The unusual habit of adult burrowing likely facilitated the diversification of these beetle‐fungus associations, enabling them to use the biomass‐rich resource that trees represent and set the stage for at least one origin of eusociality.     

Guild structure of ambrosia beetles attacking a deciduous oak tree Quercus serrata in relation to wood oldness and seasonality in three locations in the Central Japan

In order to determine factors influencing ambrosia beetle guilds on Quercus serrata, we investigated ambrosia beetles guilds by using Q. serrata bait logs in three locations in the Central Japan. Timing of cutting trees and timing of exposure were artificially controlled. Influences of location, timing of cutting, timing of exposure and wood oldness on species richness, abundances and guild structure were analyzed. Species richness and abundance peaked on bolts prepared in April–May, on bolts exposed in July, and on 2–3‐month‐old bolts. Eliminating greatest influences of location on abundance, results of hierarchical partitioning showed that timing of cutting trees had a strong influence on both species richness and abundance. LOC‐A (Aichi), in which Japanese oak wilt disease incidence occurred, showed the greatest species richness and the smallest value of Pielou's evenness. Abundance of the most major species was more than twice that of the second major species, which was a likely cause of the smallest evenness in LOC‐A. Trees killed by the Japanese oak wilt disease may have increased the abundance of the major species. On the contrary, in LOC‐C (Chichibu), alpha and beta diversity both given by Shannon index and Pielou's evenness were greatest among the three locations although species richness was smallest. High similarity between guilds in LOC‐A and LOC‐B (Chiba) was probably caused by similarity in vegetation. The location had the greatest effect on determining guild structure. Effect of timing of exposure was greater than timing of cutting. The effect of wood oldness was negligible. A hierarchical structure among the three factors was a likely cause of their relative importance determining guild structure.     

A mid-Cretaceous ambrosia fungus, Paleoambrosia entomophila gen. nov. et sp. nov. (Ascomycota: Ophiostomatales) in Burmese (Myanmar) amber,and evidence for a femoral mycangium

An ambrosia fungus is described from filamentous sporodochia adjacent to a wood–boring ambrosia beetle (Coleoptera: Curculionidae: Platypodinae) in mid-Cretaceous Burmese amber. Yeast-like propagules and hyphal fragments of Paleoambrosia entomophila gen. nov. et sp. nov. occur in glandular sac mycangia located inside the femur of the beetle. This is the first record of a fossil ambrosia fungus, showing that symbiotic associations between wood–boring insects and ectosymbiotic fungi date back some 100 million years ago. The present finding moves the origin of fungus-growing by insects from the Oligocene to the mid-Cretaceous and suggests a Gondwanan origin.     

Mating disruption of the ambrosia beetle Megaplatypus mutatus in poplar and hazelnut plantations using reservoir systems for pheromones

Megaplatypus mutatus (Chapuis) (Coleoptera: Curculionidae: Platypodinae) is an ambrosia beetle native to South America, but it has recently been introduced into Italy and represents a serious problem in commercial poplar and fruit tree plantations. Male M. mutatus emit a sex pheromone composed of (+)‐6‐methyl‐5‐hepten‐2‐ol [(+)‐sulcatol], 6‐methyl‐5‐hepten‐2‐one (sulcatone), and 3‐pentanol. We performed three field trials of mating disruption of M. mutatus in hazelnut and poplar plantations in Argentina and Italy. To perform these tests, we made plastic pheromone reservoir‐type dispensers for sulcatol, sulcatone, and 3‐pentanol with zero‐order kinetics that were deployed in the field during the female flight period. The number of galleries where mating took place was significantly higher in control than in treated areas, indicating that pheromone application had interfered with female behavior and male localization. Because damage reduction was >56% in both countries, these results demonstrate the potential for the strategy of pheromone‐mediated mating disruption of M. mutatus in commercial poplar and hazelnut plantations. Also, our study provides the first evidence for successful pheromone‐mediated mating disruption in a forest beetle.