Complex patterns of global spread in invasive insects: eco-evolutionary and management consequences

The advent of simple and affordable tools for molecular identification of novel insect invaders and assessment of population diversity has changed the face of invasion biology in recent years. The widespread application of these tools has brought with it an emerging understanding that patterns in biogeography, introduction history and subsequent movement and spread of many invasive alien insects are far more complex than previously thought. We reviewed the literature and found that for a number of invasive insects, there is strong and growing evidence that multiple introductions, complex global movement, and population admixture in the invaded range are commonplace. Additionally, historical paradigms related to species and strain identities and origins of common invaders are in many cases being challenged. This has major consequences for our understanding of basic biology and ecology of invasive insects and impacts quarantine, management and biocontrol programs. In addition, we found that founder effects rarely limit fitness in invasive insects and may benefit populations (by purging harmful alleles or increasing additive genetic variance). Also, while phenotypic plasticity appears important post-establishment, genetic diversity in invasive insects is often higher than expected and increases over time via multiple introductions. Further, connectivity among disjunct regions of global invasive ranges is generally far higher than expected and is often asymmetric, with some populations contributing disproportionately to global spread. We argue that the role of connectivity in driving the ecology and evolution of introduced species with multiple invasive ranges has been historically underestimated and that such species are often best understood in a global context

Biological control of forest plantation pests in an interconnected world requires greater international focus

The worldwide homogenization of genetic resources used in plantation forestry (primarily Pinus, Eucalypus, Populus and Acacia spp.) together with accelerating rates of human-aided dispersal of exotic pests, is resulting in plantation pests becoming broadly distributed extremely quickly, sometimes reaching a global distribution within a decade. This unprecedented rate of establishment and spread means that the risk associated with new and emerging pests is shared globally. Biological control represents a major component of the strategy to mitigate such risk, but the current efforts and scope for developing such controls are woefully inadequate for dealing with the increasing rates of pest spread. Given the global nature of the problem, biological control would benefit enormously from an international, collaborative focus. Though inherent difficulties and potential pitfalls exist, opportunities for costsharing, growth and maintenance of resources and capacity, and more comprehensive research programmes are critical to the long-term success of biological control. Governments and industries will need to increase their strategic investment in structures specifically designed to promote such focus if they are to successfully protect their forest resources.The Tree Protection Co-operative Programme (TPCP), the THRIP initiative of the Department of Trade and Industry and the National Research Foundation, South Africa.http://www.tandfonline.com/loi/ttpm20ab201

Inferring controls on the epidemiology of beech bark disease from spatial patterning of disease organisms

1 Spatial pattern in the distribution and abundance of organisms is an emergent property of collective rates of reproduction, survival and movement of individuals in a heterogeneous environment. 2 The form, intensity and scale of spatial patterning can be used to test hypotheses regarding the relative importance of candidate processes to population dynamics. 3 Using 84 plots across eastern North America, we studied populations of two associated plant parasites, the invasive felted beech scale Cryptococcus fagisuga Lind. and the native Neonectria fungi, which together cause beech bark disease (BBD). 4 We evaluated spatial patterns at the scales of trees within stands, stands within the forest and forests within the landscape to examine four hypothetically important factors in the ecology of the disease: (i) local contagion within stands; (ii) regional contagion, or among patch infection–reinfection dynamics; (iii) variation in host susceptibility linked to genetic and/or environmental heterogeneity; and (iv) climate effects on population growth of BBD organisms. 5 Analyses revealed an unexpected lack of spatial aggregation in BBD populations among trees, stands and forests. This implies that propagule pressure is generally sufficiently high throughout the infested region of North America such that neither trees nor stands are spared from the disease by dispersal limitations of the disease agents. Furthermore, variation in tree and stand level susceptibility has minimal impact on BBD dynamics and climate is not a conspicuous driver of abundance within the core range of BBD.This work was partially supported by the USDA Forest Service Northeastern Research Station, grant 04-JV-11242328-122.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1461-9563/hb2013ab201

Biology and rearing of Cleruchoides noackae (Hymenoptera : Mymaridae), an egg parasitoid for the biological control of Thaumastocoris peregrinus (Hemiptera : Thaumastocoridae)

Cleruchoides noackae Lin and Huber (Hymenoptera: Mymaridae) is a solitary egg parasitoid of Thaumastocoris peregrinus Carpintero and Dellapé (Hemiptera: Thaumastocoridae). The parasitoid was first described in 2009 and its biology and rearing are poorly understood. A key obstacle to the use of C. noackae as a biological control agent has been the ability to consistently rear it under quarantine conditions. This study reports on a series of experiments conducted in quarantine to rear C. noackae and to examine the effects of diet on longevity, per capita reproduction, and progeny sex ratio, as well as to determine development time, and preference and suitability of host eggs of different ages. When supplemented with honey solution, the longevity of C. noackae females increased significantly by 2.4 d and that of males by 1.7 d, relative to the unfed adults. Mean per capita reproduction for the honey-fed wasps was 7.7 offspring per female, with progeny sex ratio slightly skewed toward males. Mean percentage parasitism was 32.2%. C. noackae was capable of parasitizing and completing development from oviposition to adult eclosion within 15.7 d in host eggs between 0 and 5 d old. The ability of C. noackae to parasitize a wide range of host egg ages increases the period of vulnerability of T. peregrinus to attack, increasing its potential efficacy as a biological control agent. The methods and results reported here represent a crucial step in the ongoing efforts to develop this potential biological control system.The Tree Protection Co-operative Programme (TPCP), Kenya Forestry Research Institute (KEFRI) and the University of Pretoria, South Africa.http://esa.publisher.ingentaconnect.com/content/2015-10-31hb2013ab201

Parallel host range expansion in two unrelated cossid moths infesting Eucalyptus nitens on two continents

1. Two cossid moths, Coryphodema tristis and Chilecomadia valdiviana, have recently become pests on Eucalyptus nitens in South Africa and Chile, respectively. Both C. tristis and C. valdiviana have large host ranges and high levels of similarity in their host distributions. Their infestations of E. nitens are the first records of these moths on Myrtaceae. 2. The contemporaneous adoption of E. nitens as a novel host, despite widespread availability of native and introduced Myrtaceae, suggests a non-random pattern of invasion. Phylogenetic relatedness among the two species linked to cryptic invasion of one or both moths at some time in the recent past provides a possible explanation for this pattern. 3. To test this hypothesis, variation in mtDNA sequences for the COI gene of C. tristis and C. valdiviana were analyzed. The COI mtDNA sequence data showed that C. tristis and C. valdiviana are highly divergent genetically, indicating that both are native on their respective continents with independent evolutionary trajectories. 4. The parallel host range expansions to E. nitens on different continents appear to be unrelated events, likely driven by characteristics of the biology and / or ecology of the host.The Tree Protection Cooperative Programme (TPCP) and the Department of Science and Technology (DST)/ National Research Foundation (NRF) Center of Excellence in Tree Health Biology.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2311/am201

Lack of fidelity revealed in an insect-fungal mutualism after invasion

Symbiont fidelity is an important mechanism in the evolution and stability of mutualisms. Strict fidelity has been assumed for the obligate mutualism between Sirex woodwasps and their mutualistic Amylostereum fungi. This assumption has been challenged in North America where a European woodwasp, Sirex noctilio, and its fungal symbiont Amylostereum areolatum, have recently been introduced. We investigate the specificity of the mutualism between Sirex and Amylostereum species in Canada, where S. noctilio co-infests Pinus with native S. nigricornis and its mutualist A. chailletii. Using phylogenetic and culture methods, we show that extensive, reciprocal exchange of fungal species and strains is occurring, with 75.3% of S. nigricornis carrying A. areolatum and 3.5% of S. noctilio carrying A. chailletii. These findings show that the apparent specificity of the mutualism between Sirex spp. and their associated Amylostereum spp. is not the result of specific biological mechanisms that maintain symbiont fidelity. Rather, partner switching may be common when shifting geographic distributions driven by ecological or anthropogenic forces bring host and mutualist pairs into sympatry. Such novel associations have potentially profound consequences for fitness and virulence. Symbiont sharing, if it occurs commonly, may represent an important but overlooked mechanism of community change linked to biological invasions.The Tree Protection Cooperative Programme (TPCP), the Department of Trade and Industry (DTI) THRIP programme and the National Research Foundation (NRF) of South Africa.http://publishing.royalsociety.org/index.cfm?page=1566hb201

Increasing numbers and intercontinental spread of invasive insects on eucalypts

Native to Australasia, Eucalyptus (sensu lato) is one of the most planted genera of trees in the world. However, the sustainability of Eucalyptus species as plantation trees in non-native areas is increasingly threatened by the introduction and spread of Eucalyptus-feeding insects from Australia. We examine patterns and potential trends with respect to the global spread of Eucalyptus-feeding insects. Likely pathways of introduction and drivers of the rapid distribution of these insects, as well as management options are considered. The rate of introductions is shown to have increased nearly fivefold since the 1980s. As a result, the number of non-native pests of eucalypts outside of Australia has doubled in less than three decades. Furthermore, the rate of secondary spread among continents has also increased. Surprisingly, we found no association between area planted and the number of pests or new introductions. Only a small number of countries have been the points of first detection outside the native range; these countries have acted as bridgeheads to other regions. Quarantine regulations aimed at reducing the spread of invasive organisms appear to be ineffective at a global scale, and pathways allowing these invasions to occur are poorly understood or unknown. An expanded suite of management options are needed to provide resilience against the rapid accrual and homogenization of eucalypt pests, thereby ensuring the sustainability of eucalypt forestry worldwide.Tree Protection Cooperative Programme (TPCP), the National Research Foundation (NRF) and the Department of Trade and Industry (DTI) of South Africa.http://link.springer.com/journal/105302017-04-30hb2016Forestry and Agricultural Biotechnology Institute (FABI)GeneticsZoology and Entomolog

Distribution and diversity of Phytophthora across Australia

The introduction and subsequent impact of Phytophthora cinnamomi within native vegetation is one of the major conservation issues for biodiversity in Australia. Recently, many new Phytophthora species have been described from Australia's native ecosystems; however, their distribution, origin, and potential impact remain unknown. Historical bias in Phytophthora detection has been towards sites showing symptoms of disease, and traditional isolation methods show variable effectiveness of detecting different Phytophthora species. However, we now have at our disposal new techniques based on the sampling of environmental DNA and metabarcoding through the use of high-throughput sequencing. Here, we report on the diversity and distribution of Phytophthora in Australia using metabarcoding of 640 soil samples and we compare the diversity detected using this technique with that available in curated databases. Phytophthora was detected in 65% of sites, and phylogenetic analysis revealed 68 distinct Phytophthora phylotypes. Of these, 21 were identified as potentially unique taxa and 25 were new detections in natural areas and/or new introductions to Australia. There are 66Phytophthora taxa listed in Australian databases, 43 of which were also detected in this metabarcoding study. This study revealed high Phytophthora richness within native vegetation and the additional records provide a valuable baseline resource for future studies. Many of the Phytophthora species now uncovered in Australia's native ecosystems are newly described and until more is known we need to be cautious with regard to the spread and conservation management of these new species in Australia's unique ecosystems

Demography of an invading forest insect reunited with hosts and parasitoids from its native range

SUPPLEMENTARY MATERIALS : Explanation note: This file includes demographic data from native Sirex nigricornis woodwasps that were collected during our study. TABLE S1. Correlation matrix of bolt-level variables for P. resinosa and P. sylvestris. TABLE S2. Review of 10th and 90th percentile female body mass from insect species estimated from source paper cited, showing comparatively higher female S. noctilio body size variation. FIGURE S1. Examples of S. noctilio oviposition sites, lesion formation and emergence holes in the field. FIGURE S2. Top panels show a typical bolt from P. sylvestris with bark removed and S. noctilio emergence holes and oviposition sites identified. FIGURE S3. The number of S. noctilio emerging per tree was best described by a zero inflated negative binomial distribution (dotted line) with proportion of excess zeroes Φ = 0.32, μ = 75.39 and overdispersion parameter k = 0.35. FIGURE S4. Allometric relationships for S. noctilio in the Central NY data set: number of eggs and adult female mass (a; quantile regression), adult female mass and adult female length (b; fitted power function) and adult length and width of adult head capsule (c; linear regression).The Sirex woodwasp Sirex noctilio Fabricius (Hymenoptera: Siricidae), a widespread invasive pest of pines in the Southern Hemisphere, was first detected in North America in 2004. This study assessed the impacts of life history traits, host resistance and species interactions on the demography of S. noctilio in New York, Pennsylvania and Vermont, then compared key metrics to those found in the native range in Galicia, Spain. Many trees naturally attacked by S. noctilio in North America produced no adult woodwasps, with 5 of 38 infested trees (13%) sampled across six sites yielding 64% of emerging insects. Reproductive success was highest in the introduced host scots pine, Pinus sylvestris, but native red pine, Pinus resinosa, produced larger insects. Sirex noctilio required one or sometimes two years to develop and sex ratios were male biased, 1:2.98 ♀:♂. Body size and fecundity were highly variable, but generally lower than observed in non-native populations in the Southern Hemisphere. Hymenopteran parasitoids killed approximately 20% of S. noctilio larvae and 63% of emerging adults were colonized by the parasitic nematode Deladenus siricidicola, although no nematodes entered eggs. Demographic models suggested that S. noctilio in the northeastern USA have a higher potential for population growth than populations in the native range: estimated finite factor of increase, λ, was 4.17–4.52 (depending on tree species colonized), compared to λ = 1.57 in Spain.USDA Forest Service International Programs and OP RDE.https://neobiota.pensoft.netam2023Forestry and Agricultural Biotechnology Institute (FABI)Zoology and Entomolog

Predictors of Phytophthora diversity and community composition in natural areas across diverse Australian ecoregions

Comprehensive understanding of the patterns and drivers of microbial diversity at a landscape scale is in its infancy, despite the recent ease by which soil communities can be characterized using massively parallel amplicon sequencing. Here we report on a comprehensive analysis of the drivers of diversity distribution and composition of the ecologically and economically important Phytophthora genus from 414 soil samples collected across Australia. We assessed 22 environmental and seven categorical variables as potential predictors of Phytophthora species richness, α and β diversity, including both phylogenetically and non‐phylogenically explicit methods. In addition, we classified each species as putatively native or introduced and examined the distribution with respect to putative origin. The two most widespread species, P. multivora and P. cinnamomi, are introduced, though five of the ten most widely distributed species are putatively native. Introduced taxa comprised over 54% of Australia's Phytophthora diversity and these species are known pathogens of annual and perennial crop habitats as well as urban landscapes and forestry. Patterns of composition were most strongly predicted by bioregion (R2 = 0.29) and ecoregion (R2 = 0.26) identity; mean precipitation of warmest quarter, mean temperature of the wettest quarter and latitude were also highly significant and described approximately 21, 14 and 13% of variation in NMDS composition, respectively. We also found statistically significant evidence for phylogenetic over‐dispersion with respect to key climate variables.This study provides a strong baseline for understanding biogeographical patterns in this important genus as well the impact of key plant pathogens and invasive Phytophthora species in natural ecosystems