Are traded forest tree seeds a potential source of nonnative pests?

The international seed trade is considered relatively safe from a phytosanitary point of view and is therefore less regulated than trade in other plants for planting. However, the pests carried by traded seeds are not well known. We assessed insects and fungi in 58 traded seed lots of 11 gymnosperm and angiosperm tree species from North America, Europe, and Asia. Insects were detected by X-raying and molecular methods. The fungal community was characterized using high-throughput sequencing (HTS) and by growing fungi on non-selective agar. About 30% of the seed lots contained insect larvae. Gymnosperms contained mostly hymenopteran (Megastigmus spp.) and dipteran (Cecidomyiidae) larvae, while angiosperms contained lepidopteran (Cydia latiferreana) and coleopteran (Curculio spp.) larvae. HTS indicated the presence of fungi in all seed lots and fungi grew on non-selective agar from 96% of the seed lots. Fungal abundance and diversity were much higher than insect diversity and abundance, especially in angiosperm seeds. Almost 50% of all fungal exact sequence variants (ESVs) found in angiosperms were potential pathogens, in comparison with around 30% of potentially pathogenic ESVs found in gymnosperms. The results of this study indicate that seeds may pose a greater risk of pest introduction than previously believed or accounted for. A rapid risk assessment suggests that only a small number of species identified in this study is of phytosanitary concern. However, more research is needed to enable better risk assessment, especially to increase knowledge about the potential for transmission of fungi to seedlings and the host range and impact of identified species.

Phylogeography of the Spanish Moon Moth Graellsia isabellae (Lepidoptera, Saturniidae).

BACKGROUND: Geographic and demographic factors as well as specialisation to a new host-plant may lead to host-associated differentiation in plant-feeding insects. We explored the phylogeography of a protected moth, Graellsia isabellae, and its two recognised host-plant species (Pinus sylvestris and P. nigra) in order to seek for any concordance useful to disentangle the evolutionary history of this iconic lepidopteran. RESULTS: DNA variation in one mitochondrial marker and nine nuclear microsatellite loci revealed a strong phylogeographic pattern across 28 populations of G. isabellae studied in Spain and France comprising six groups mostly distributed along different mountain ranges. Reanalysis of a previously published chloroplast microsatellite dataset revealed a three and two-group structure for Spanish P. sylvestris and P. nigra, respectively. Overall, the population groupings of this protected moth did not match the ones of P. sylvestris and P. nigra. CONCLUSIONS: There was no evidence of host-associated differentiation between populations using P. sylvestris and the ones inhabiting P. nigra. The two major mitochondrial clades of G. isabellae likely diverged before the Last Glacial Maximum and geographically separated the species into a "southern" (Central and Southern Iberian clusters) and a "northern" lineage (Eastern Iberian, Pyrenean and French Alpine clusters). The Eastern Iberian System, where this insect uses both host-plants, harboured the highest level of genetic diversity. Such a group independently colonised the West and East parts of the Pyrenees. Our results point to a native origin for the French populations occurring in the Alps, genetically related to the Eastern Iberian and Pyrenean sites. The Central Iberian group derived from Southern Iberian ancestors. Secondary contacts were inferred between the Southern/Central Iberian populations and Eastern Iberian cluster as well as between the two Pyrenean ones. The mito-nuclear discordance observed with regard to the Eastern Iberian cluster is congruent with a secondary contact after the evolution of mito-nuclear incompatibilities in geographically isolated areas.

Climate, host and geography shape insect and fungal communities of trees.

Non-native pests, climate change, and their interactions are likely to alter relationships between trees and tree-associated organisms with consequences for forest health. To understand and predict such changes, factors structuring tree-associated communities need to be determined. Here, we analysed the data consisting of records of insects and fungi collected from dormant twigs from 155 tree species at 51 botanical gardens or arboreta in 32 countries. Generalized dissimilarity models revealed similar relative importance of studied climatic, host-related and geographic factors on differences in tree-associated communities. Mean annual temperature, phylogenetic distance between hosts and geographic distance between locations were the major drivers of dissimilarities. The increasing importance of high temperatures on differences in studied communities indicate that climate change could affect tree-associated organisms directly and indirectly through host range shifts. Insect and fungal communities were more similar between closely related vs. distant hosts suggesting that host range shifts may facilitate the emergence of new pests. Moreover, dissimilarities among tree-associated communities increased with geographic distance indicating that human-mediated transport may serve as a pathway of the introductions of new pests. The results of this study highlight the need to limit the establishment of tree pests and increase the resilience of forest ecosystems to changes in climate.

Worldwide diversity of endophytic fungi and insects associated with dormant tree twigs.

International trade in plants and climate change are two of the main factors causing damaging tree pests (i.e. fungi and insects) to spread into new areas. To mitigate these risks, a large-scale assessment of tree-associated fungi and insects is needed. We present records of endophytic fungi and insects in twigs of 17 angiosperm and gymnosperm genera, from 51 locations in 32 countries worldwide. Endophytic fungi were characterized by high-throughput sequencing of 352 samples from 145 tree species in 28 countries. Insects were reared from 227 samples of 109 tree species in 18 countries and sorted into taxonomic orders and feeding guilds. Herbivorous insects were grouped into morphospecies and were identified using molecular and morphological approaches. This dataset reveals the diversity of tree-associated taxa, as it contains 12,721 fungal Amplicon Sequence Variants and 208 herbivorous insect morphospecies, sampled across broad geographic and climatic gradients and for many tree species. This dataset will facilitate applied and fundamental studies on the distribution of fungal endophytes and insects in trees.

Diapause Regulation in Newly Invaded Environments: Termination Timing Allows Matching Novel Climatic Constraints in the Box Tree Moth, Cydalima perspectalis (Lepidoptera: Crambidae).

The association between indirect environmental cues that modulate insect diapause and the actual stressors is by no means granted when a species encounters new environments. The box tree moth, Cydalima perspectalis, is an Asian pest whose rapid invasion in Europe causes considerable economic and ecological impacts. Larvae enter a winter diapause induced by the photoperiod in both native and invaded ranges, but factors that trigger the return to an active phase are still unknown. Yet, identifying them is crucial to understand how diapause end synchronizes with the end of the winter stress encountered in Europe. To test whether activity resumption is regulated by thermal and/or photoperiodic thresholds, or additive effects between these factors often involved in diapause termination, diapausing caterpillars from an invaded area were exposed to crossed treatments at the laboratory. The evolution of diapause rate was monitored over time and compared to that of nearby field sites invaded. A strong positive effect of increasing temperature was found on the rate and dynamics of diapause termination, whereas no compelling effect of photoperiod appeared. Resuming development directly when main stressors fade, not in response to indirect photoperiodic cues that could be mismatched outside native areas, likely contributes to the good match observed between diapause and the new climates that this pest encountered in the invaded range.

The sex pheromones of two pine sawfly species, Gilpinia frutetorum and Gilpinia socia: chemical identification, synthesis and biological activity.

3,7-Dimethylpentadecan-2-ol and 3-methylpentadecan-2-ol were identified in female whole body extracts from the two pine sawfly species Gilpinia frutetorum and Gilpinia socia. This is the first observation of 3-methylpentadecan-2-ol in extracts of a female pine sawfly species. Synthetic and highly pure stereoisomers of 3,7-dimethylpentadecan-2-ol and 3-methylpentadecan-2-ol were used to verify that the (2S,3R,7R)-isomer of 3,7-dimethylpentadecan-2-ol and (2S,3R)-3-methylpentadecan-2-ol were present in the extracts. The four stereoisomers of 3-methylpentadecan-2-ol and their biologically active esters were produced via chemoenzymatic methods and the synthesis is described in detail. Male G. socia antennae responded strongly in EAG recordings to the (2S,3R)-isomer of the acetate and propionate of 3-methylpentadecan-2-ol. Male antennae of both G. frutetorum and G. socia also responded to the (2S,3R,7R)- and (2S,3R,7S)-acetates of 3,7-dimethylpentadecan-2-ol.

Genetic Variation and Differentiation of Hylesia metabus (Lepidoptera: Saturniidae): Moths of Public Health Importance in French Guiana and in Venezuela.

Hylesia moths impact human health in South America, inducing epidemic outbreaks of lepidopterism, a puriginous dermatitis caused by the urticating properties of females' abdominal setae. The classification of the Hylesia genus is complex, owing to its high diversity in Amazonia, high intraspecific morphological variance, and lack of interspecific diagnostic traits which may hide cryptic species. Outbreaks of Hylesia metabus have been considered responsible for the intense outbreaks of lepidopterism in Venezuela and French Guiana since the C20, however, little is known about genetic variability throughout the species range, which is instrumental for establishing control strategies on H. metabus. Seven microsatellites and mitochondrial gene markers were analyzed from Hylesia moths collected from two major lepidopterism outbreak South American regions. The mitochondrial gene sequences contained significant genetic variation, revealing a single, widespread, polymorphic species with distinct clusters, possibly corresponding to populations evolving in isolation. The microsatellite markers validated the mitochondrial results, and suggest the presence of three populations: one in Venezuela, and two in French Guiana. All moths sampled during outbreak events in French Guiana were assigned to a single coastal population. The causes and implications of this finding require further research.

Modelling the impact of an invasive insect via reaction-diffusion.

An exotic, specialist seed chalcid, Megastigmus schimitscheki, has been introduced along with its cedar host seeds from Turkey to southeastern France during the early 1990s. It is now expanding in plantations of Atlas Cedar (Cedrus atlantica). We propose a model to predict the expansion and impact of this insect. This model couples a time-discrete equation for the ovo-larval stage with a two-dimensional reaction-diffusion equation for the adult stage, through a formula linking the solution of the reaction-diffusion equation to a seed attack rate. Two main diffusion operators, of Fokker-Planck and Fickian types, are tested. We show that taking account of the dependence of the insect mobility with respect to spatial heterogeneity, and choosing the appropriate diffusion operator, are critical factors for obtaining good predictions.

Sentinel nurseries to assess the phytosanitary risks from insect pests on importations of live plants.

Ornamental plants represent a major pathway of invasion for alien pests worldwide. Commodity risk analyses are carried out to assess the risk posed by a new trade in a commodity, but they are restricted by our limited knowledge of the pests carried by traded plants. We used the sentinel nursery technique to identify insects attacking woody plants imported into Europe. We established two sentinel nurseries in China, with five traded Asian plants. These nurseries were monitored for two years to obtain lists of insects that can be expected on these commodities. These records were compared with those obtained from literature surveys, which are usually the sources of information available to pest risk assessors. At each site, 105 insect species and host associations were found on sentinel plants and 90% of these associations had not been found in a previous literature survey of insect pests of the five plants. Nearly 80% of these associations were not found in an a posteriori literature survey. An assessment classified 9%, 7% and 84% of the insect records as presenting a high, moderate and low likelihood of introduction, respectively. These results show the benefit of sentinel nurseries to identify potential infestation of plant commodity imports.

Megastigmus seed chalcids (Hymenoptera, Torymidae) radiated much more on Angiosperms than previously considered. I- Description of 8 new species from Kenya, with a key to the females of Eastern and Southern Africa.

A survey of seed chalcids from woody plants in Kenya revealed 12 species belonging to the genus Megastigmus Dalman, 1820, and has increased to 16 the number of Megastigmus species presently recorded from the Afrotropical Region, of which at least 13 are seed feeders. A key to female Megastigmus of the Afrotropical Region is provided. Eight new species are described from morphological evidence: Megastigmus lanneae Roques & Copeland, Megastigmus laventhali Roques & Copeland, Megastigmus ozoroae Roques & Copeland, and Megastigmus smithi Roques & Copeland in seeds of species of the family Anacardiaceae, Megastigmus copelandi Roques & Copeland and Megastigmus grewianae Roques & Copeland in seeds of Malvaceae, Megastigmus helinae Roques & Copeland in seeds of Rhamnaceae, and Megastigmus icipeensis Roques & Copeland for which no host is known. These collections include the first records of Malvaceae and Rhamnaceae as hosts of Megastigmus seed chalcids, which appear to have radiated in Angiosperms much more than previously considered. Analyses of the mitochondrial (cytochrome oxidase subunit one - COI) and nuclear DNA (28S ribosomal region) could be carried out on 8 of the 16 African species of which 5 were newly described ones. The species associated with Anacardiaceae always clustered together in phylogenies, confirming the existence of a strong and ancestral monophyletic clade, unlike the ones associated with Malvaceae and Rhamnaceae, whose position remains unclear. All holotypes are deposited in the National Museums of Kenya.