Ribeiro-Correia, J. P. | Search bioRxiv

bioRxiv2025

Worldwide spread of Hylurgus ligniperda (Coleoptera: Scolytinae), and the potential role of bridgehead invasions

Hylurgus ligniperda (F.) is a highly successful invader among bark beetles (Scolytinae) and forest insects in general. Native to the western Palearctic region, it has become established in every continent where its host plants (Pinus spp.) occur. Especially in southern hemisphere regions with large pine plantations, it is often highly abundant. As a repeat invader with a wealth of information on various aspects relevant for biological invasions, it is highly suitable as a model organism for studying the role of international trade, the planting of non-native trees, and the potential occurrence of bridgehead invasions (where abundant non-native populations precipitate further invasions). In the present study, our specific objectives were to reconstruct the worldwide invasions of H. ligniperda and the pathways involved by using a multi-pronged approach including population genetics, analysis of historic interception data generated from inspections of imports, and records of establishments in the literature. Our review of the native and non-native ranges of H. ligniperda and the chronology of establishments revealed at least 13 separate invasions of non-native regions, beginning with Madeira (Portugal) before 1850, and, most recently, eastern China in 2019. We compared the population genetics of 464 specimens from eight countries in the native range and eight countries in the non-native range. Sequencing of the mitochondrial COI gene revealed the presence of 29 haplotypes in six well-supported clades, based on a Bayesian analysis. Non-native populations had significantly lower haplotype diversity (mean h = 0.219) than populations in the native range (mean h = 0.691). Countries in the non-native range had an average of about two haplotypes compared with about four haplotypes in native countries. In the non-native range, only one or two haplotypes were dominant, and these differed among invaded regions except for haplotype HL-H3 which occurred in Australia, New Zealand and China as well as in four countries in southern Europe, and HL-H4 which was dominant in New Zealand, California, New York State, and eastern China as well as two countries in southern Europe. Analyses of interceptions of H. ligniperda with imports arriving in five countries revealed that between 74% and 99% of interceptions originated from other non-native regions while in the USA, most interceptions were linked to imports from the native range beginning in the 1970s. Based on the combined evidence of the chronology of invasions, interception data, and analysis of haplotype distribution, we conclude that the early invasions (before 1950) probably all originated from the native range, while several of the more recent invasions probably originated from parts of the non-native range (suggestive of a bridgehead effect). However, it cannot be determined with certainty what the original sources of each of the invading populations were.

ecology↗

bioRxiv2023

Distribution of the invasive Anisandrus maiche (Coleoptera: Scolytinae) in Switzerland, first record in Europe of its ambrosia fungus Ambrosiella cleistominuta, and its new association with Xylosandrus crassiusculus

In 2022, two independent insect surveys in canton Ticino (southern Switzerland) revealed the widespread occurrence of the invasive ambrosia beetle Anisandrus maiche from southern to central-upper Ticino. This species is native to east Asia and has previously been found as a non-native invasive species in the United States, Canada, western Russia, Ukraine and, in 2021, in northern Italy. Here, we present the results of several trapping studies using different trap types (bottle traps, funnel traps and Polytrap intercept traps) and attractants and a map of the distribution of the species. In total, 685 specimens of A. maiche, all female, were trapped, and the identity of selected individuals was confirmed by morphological and molecular identification based on three mitochondrial and nuclear markers (COI, 28S and CAD). Traps checked from early April to early September 2022 in intervals of two to four weeks showed that flights of A. maiche occurred mainly from June to mid-August. Isolation of fungal associates of A. maiche from beetles trapped alive revealed the presence of four fungal species, including the ambrosia fungus Ambrosiella cleistominuta, the known mutualists of A. maiche. The identity of A. cleistominuta was confirmed by comparing DNA sequences of its nuclear, internal transcribed spacer (ITS) gene with reference sequences in NCBI and BOLDSYSTEMS. This represents the first record of A. cleistominuta in Europe. Ambrosiella cleistominuta was also found in association with another non-native invasive ambrosia beetle, Xylosandrus crassiusculus, at a botanic garden in central Ticino. As ambrosia beetles usually show a high degree of fidelity with only one mutualistic fungus (in the case of X. crassiusculus normally Ambrosiella roeperi), this association is highly unusual and probably the result of lateral transfer among these non-native invasive species. Of the other fungal associates isolated from A. maiche in Ticino, Fusarium lateritium is of note as there is a possibility that A. maiche could act as a vector of this plant pathogen. We highlight several research needs that should be addressed to gain insight into the potential impact of these non-native species and to overcome problems with heteroplasmy in COI sequences in studies of invasion and population genetics of ambrosia beetles.

ecology↗