Complementarity of statistical treatments to reconstruct worldwide routes of invasion: the case of the Asian ladybird Harmonia axyridis.

Inferences about introduction histories of invasive species remain challenging because of the stochastic demographic processes involved. Approximate Bayesian computation (ABC) can help to overcome these problems, but such method requires a prior understanding of population structure over the study area, necessitating the use of alternative methods and an intense sampling design. In this study, we made inferences about the worldwide invasion history of the ladybird Harmonia axyridis by various population genetics statistical methods, using a large set of sampling sites distributed over most of the species' native and invaded areas. We evaluated the complementarity of the statistical methods and the consequences of using different sets of site samples for ABC inferences. We found that the H. axyridis invasion has involved two bridgehead invasive populations in North America, which have served as the source populations for at least six independent introductions into other continents. We also identified several situations of genetic admixture between differentiated sources. Our results highlight the importance of coupling ABC methods with more traditional statistical approaches. We found that the choice of site samples could affect the conclusions of ABC analyses comparing possible scenarios. Approaches involving independent ABC analyses on several sample sets constitute a sensible solution, complementary to standard quality controls based on the analysis of pseudo-observed data sets, to minimize erroneous conclusions. This study provides biologists without expertise in this area with detailed methodological and conceptual guidelines for making inferences about invasion routes when dealing with a large number of sampling sites and complex population genetic structures.

Risk assessment of Phlyctinus callosus for the EU.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a quantitative risk assessment for the EU of Phlyctinus callosus (Coleoptera: Curculionidae), a polyphagous pest occurring in Australia, New Zealand and South Africa. The current risk assessment focused on potential pathways for entry, the climatic conditions allowing establishment, the expected spread capacity and the impact considering a time horizon of 10 years (2023-2032). The Panel identified the import of apples, cut flowers and table grapes as the most relevant entry pathways. Over the next 10 years, an annual median estimate of approximately 49.5 (90% certainty range, CR, ranging from 4.0 to 881.2) potential P. callosus founder populations are expected. When the probability of establishment is considered and climatic indicators are used to define the areas in the EU where establishment is possible, the model estimated a median of 1 founder population every 1.3 years (90% CR: 1 every 30.8 years to 23.3 per year) in the scenario where the areas are defined by the union of all the climatic indicators and 1 founder population every 11.9 years (90% CR: 1 every 256.6 years to 2.5 per year) in the scenario where establishment is possible only in the areas defined by the climatic indicator of minimum soil temperature. The estimated number of founder populations per year is mostly driven by the probability of establishment in the rural areas, infestation rate in table grapes and the probability of transfer to a suitable host in the rural area. The risk of entry for cut flowers and apples is substantially lower than the risk from the table grapes. If such founder populations were to establish, P. callosus is estimated to spread by natural dispersal and common agricultural practices at a rate of 15.5 m/year (90% CR 5.1-46.8 m/year) after a lag phase of 4.0 years (90% CR 1.3-8.7 years). The impact, expressed as percentage loss of the production directly attributable to P. callosus in the areas where establishment is possible and assuming farmers do not apply specific control measures was estimated at 0.5% (90% CR 0.01%-2.8%) for cut flowers/foliage, 5.2% (90% CR 2.2%-11.7%) for apples and 2% (90% CR 1.3%-5.2%) for table grapes. Options for risk reduction are discussed, but their effectiveness is not quantified.

Analysis of Thaumatotibia leucotreta (Lepidoptera: Tortricidae: Olethreutinae) mitochondrial genomes in the context of a recent host range expansion.

BACKGROUND: The false codling moth (FCM), Thaumatotibia leucotreta (Meyrick, 1913), is a significant pest of various important economic crops and is a EU quarantine pest. In the last decade the pest has been reported on Rosa spp. In this study we determined whether this shift occurred within specific FCM populations across seven eastern sub-Saharan countries or whether the species opportunistically switches to this novel host as it presents itself. To achieve this, we assessed the genetic diversity of complete mitogenomes of T. leucotreta specimens intercepted at import and analysed potential linkages with the geographical origin and host species. RESULTS: Genomic, geographical and host information were integrated into a T. leucotreta Nextstrain build which contains 95 complete mitogenomes generated from material intercepted at import between January 2013 and December 2018. Samples represented seven sub-Saharan countries and mitogenomic sequences grouped in six main clades. DISCUSSION: If host strains of FCM would exist, specialization from a single haplotype towards the novel host is expected. Instead, we find specimens intercepted on Rosa spp. in all six clades. The absence of linkage between genotype and host suggests opportunistic expansion to the new host plant. This underlines risks of introducing new plant species to an area as the effect of pests already present on the new plant might be unpredictable with current knowledge.

Assessment of the probability of introduction of Thaumatotibia leucotreta into the European Union with import of cut roses.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a quantitative pest risk assessment to assess whether the import of cut roses provides a pathway for the introduction of Thaumatotibia leucotreta (Lepidoptera: Tortricidae) into the EU. The assessment was limited to the entry and establishment steps. A pathway model was used to assess how many T. leucotreta individuals would survive and emerge as adults from commercial or household wastes in an EU NUTS2 region climatically suitable in a specific season. This pathway model for entry consisted of three components: a cut roses distribution model, a T. leucotreta developmental model and a waste model. Four scenarios of timing from initial disposal of the cut roses until waste treatment (3, 7, 14 and 28 days) were considered. The estimated median number of adults escaping per year from imported cut roses in all the climatically suitable NUTS2 regions of the EU varied from 49,867 (90% uncertainty between 5,298 and 234,393) up to 143,689 (90% uncertainty between 21,126 and 401,458) for the 3- and 28-day scenarios. Assuming that, on average, a successful mating will happen for every 435 escaping moths, the estimated median number of T. leucotreta mated females per year from imported cut roses in all the climatically suitable NUTS2 regions of the EU would vary from 115 (90% uncertainty between 12 and 538) up to 330 (90% uncertainty between 49 and 923) for the 3- and 28-day scenarios. Due to the extreme polyphagia of T. leucotreta, host availability will not be a limiting factor for establishment. Climatic suitability assessment, using a physiologically based demographic modelling approach, identified the coastline extending from the northwest of the Iberian Peninsula through the Mediterranean as area suitable for establishment of T. leucotreta. This assessment indicates that cut roses provide a pathway for the introduction of T. leucotreta into the EU.

Commodity risk assessment of Momordica charantia fruits from Honduras.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. Momordica fruits originating from countries where Thrips palmi is known to occur qualify as high risk plants. This Scientific Opinion covers the introduction risk for T. palmi posed by fruits of Momordica charantia L. imported from Honduras, taking into account the available scientific information, including the technical information provided by the National Service of Agrifood Health and Safety (SENASA) of Honduras. The risk mitigation measures proposed in the technical dossier from Honduras were evaluated taking into account the possible limiting factors. An expert judgement is given on the likelihood of pest freedom taking into consideration the potential pest pressure in the field, the risk mitigation measures acting on the pest in the field and in the packinghouse, including uncertainties associated with the assessment. For T. palmi on M. charantia fruits from Honduras, an expert judgement is given on the likelihood of pest freedom following the evaluation of the risk mitigation measures acting on T. palmi, including any uncertainties. The Expert Knowledge Elicitation indicated, with 95% certainty that between 9,406 and 10,000 M. charantia fruits per 10,000 will be free from T. palmi.

Commodity risk assessment of Momordica charantia fruits from Suriname.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. M. charantia fruits originating from countries where Thrips palmi is known to occur qualify as high-risk plants. This Scientific Opinion covers the introduction risk for T. palmi posed by fruits of Momordica charantia L. imported from Suriname, taking into account the available scientific information, including the technical information provided by the National Plant Protection Organization of Suriname. The risk mitigation measures proposed in the technical dossier from Suriname were evaluated taking into account the possible limiting factors. An expert judgement is given on the likelihood of pest freedom taking into consideration the potential pest pressure in the field, the risk mitigation measures acting on the pest in the field and in the packinghouse, including uncertainties associated with the assessment. For T. palmi on M. charantia fruits from Suriname, an expert judgement is given on the likelihood of pest freedom following the evaluation of the risk mitigation measures acting on T. palmi, including any uncertainties. The Expert Knowledge Elicitation indicated, with 95% certainty that between 8,652 and 10,000 M. charantia fruits per 10,000 will be free from T. palmi.

Commodity risk assessment of Momordica charantia fruits from Sri Lanka.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. Momordica fruits originating from countries where Thrips palmi is known to occur qualify as high-risk plants. This Scientific Opinion covers the introduction risk for T. palmi posed by fruits of Momordica charantia L. imported from Sri Lanka, taking into account the available scientific information, including the technical information provided by the National Plant Quarantine Service of Sri Lanka. The risk mitigation measures proposed in the technical dossier from Sri Lanka were evaluated taking into account the possible limiting factors. An expert judgement is given on the likelihood of pest freedom taking into consideration the potential pest pressure in the field, the risk mitigation measures acting on the pest in the field and in the packing house, including uncertainties associated with the assessment. For T. palmi on M. charantia fruits from Sri Lanka, an expert judgement is given on the likelihood of pest freedom following the evaluation of the risk mitigation measures acting on T. palmi, including any uncertainties. The Expert Knowledge Elicitation indicated, with 95% certainty that between 9831 and 10,000 M. charantia fruits/10,000 will be free from T. palmi.

Commodity risk assessment of Momordica charantia fruits from Mexico.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. Momordica fruits originating from countries where Thrips palmi is known to occur qualify as high risk plants. This Scientific Opinion covers the introduction risk for T. palmi posed by fruits of Momordica charantia L. imported from Mexico, taking into account the available scientific information, including the technical information provided by the National Service of Health, Safety and Agrifood Quality (Senasica) of Mexico. The risk mitigation measures proposed in the technical dossier from Mexico were evaluated taking into account the possible limiting factors. An expert judgement is given on the likelihood of pest freedom taking into consideration the potential pest pressure in the field, the risk mitigation measures acting on the pest in the field and in the packinghouse, including uncertainties associated with the assessment. For T. palmi on M. charantia fruits from Mexico, an expert judgement is given on the likelihood of pest freedom following the evaluation of the risk mitigation measures acting on T. palmi, including any uncertainties. The Expert Knowledge Elicitation indicated, with 95% certainty that between 9,492 and 10,000 M. charantia fruits per 10,000 will be free from T. palmi.

Commodity risk assessment of Momordica charantia fruits from Thailand.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. Momordica fruits originating from countries where Thrips palmi is known to occur qualify as high-risk plants. This Scientific Opinion covers the introduction risk for T. palmi posed by fruits of Momordica charantia L. imported from Thailand, taking into account the available scientific information, including the technical information provided by the Department of Agriculture of Thailand. The risk mitigation measures proposed in the technical dossier from Thailand were evaluated taking into account the possible limiting factors. An expert judgement is given on the likelihood of pest freedom taking into consideration the potential pest pressure in the field, the risk mitigation measures acting on the pest in the field and in the packing house, including uncertainties associated with the assessment. For T. palmi on M. charantia fruits from Thailand, an expert judgement is given on the likelihood of pest freedom following the evaluation of the risk mitigation measures acting on T. palmi, including any uncertainties. The Expert Knowledge Elicitation indicated, with 95% certainty that between 9,496 and 10,000 M. charantia fruits/10,000 will be free from T. palmi.

Tracking outbreak populations of the pepper weevil Anthonomus eugenii (Coleoptera; Curculionidae) using complete mitochondrial genomes.

The pepper weevil, Anthonomus eugenii, is a major pest on Capsicum species. Apart from natural spread, there is a risk of spread via international pepper trade. In the Netherlands, a pepper weevil outbreak occurred in 2012 and affected six greenhouses producing different sweet pepper varieties. The following year, a pepper weevil outbreak occurred in Italy. To trace the origin of the Dutch outbreak and to establish if the Dutch and Italian outbreaks were linked, we determined the mitogenomes of A. eugenii specimens collected at outbreak locations, and compared these with specimens from the native area, and other areas where the pest was introduced either by natural dispersal or via trade. The circular 17,257 bp A. eugenii mitogenome comprises thirteen mitochondrial genes typically found in insect species. Intra-species variation of these mitochondrial genes revealed four main mitochondrial lineages encompassing 41 haplotypes. The highest diversity was observed for specimens from its presumed native area (i.e. Mexico). The Dutch outbreak specimens represented three highly similar haplotypes, suggesting a single introduction of the pest. The major Dutch haplotype was also found in two specimens from New Jersey. As the Netherlands does not have pepper trade with New Jersey, it is likely that the specimens sampled in New Jersey and those sampled in the Netherlands originate from a shared source that was not included in this study. In addition, our analysis shows that the Italian and Dutch outbreaks were not linked. The mitochondrial genome is a useful tool to trace outbreak populations and the methodology presented in this paper could prove valuable for other invasive pest species, such as the African fruit moth Thaumatotibia leucotreta and emerald ash borer Agrilus planipennis.

Early wound reactions of Japanese maple during winter dormancy: the effect of two contrasting temperature regimes.

During winter dormancy, temperate trees are capable of only a restricted response to wounding. Depending on the ambient temperature during winter dormancy, wounded trees may start compartmentalization, e.g. by producing inhibitory compounds, but it is thought that processes involving cell proliferation, such as the formation of callus and wound xylem, are delayed until the next growing season. We investigated the effect of two contrasting temperature regimes on early reactions of Acer palmatum trees to wounding during winter bud dormancy. Stems of A. palmatum trees were wounded and stored under an ambient temperature of 4 or 15 °C for 3 weeks during winter bud dormancy. We then studied wound reactions in the living bark, cambial region and xylem. In the 4 °C treatment, wound reactions were virtually absent. In the 15 °C treatment, however, trees reacted to wounding by dieback of the cortex and phloem and by the formation of ligno-suberized layers. In the cambial zone, cambial dieback occurred and callus tissue and wound xylem were formed locally, close to the wound margins. In the xylem, compartmentalization took place by deposition of inhibitory compounds in fibre cells and vessel elements. We conclude that temperature is an important factor in wound reactions during winter dormancy, and may even induce proliferation of callus and wound xylem within a 3-week period. It therefore seems likely that trees that have been wounded during dormancy in areas with mild or warm winters might cope better with wounding, as unlike trees in cold environments, they may compartmentalize wounds even during winter dormancy.