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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.

Live plants are often traded in winter or early spring when the number of pests is potentially low, in part because deciduous trees lack foliage. However, the pests that may be associated with traded dormant plant material are likely to be largely unknown. Pest risk assessments can only be performed for known pest species and it is therefore important to identify potential pests before they are moved to a new area. In addition, it is difficult to predict whether introduced pests, even if already well known, may shift host after their arrival. Several studies attempted to estimate the likelihood of host shifts using literature about known pest-host associations, but the number of pests in these studies was often limited and the data were unlikely collected in the same place and at the same time. To overcome these problems, we performed a global study which aimed at detecting potential insect pests and fungal pathogens on congeneric native and exotic woody plant species that belong to six studied tree genera. Sampling was done simultaneously in 33 countries around the world following a common sampling protocol. At each location, twenty 50 cm long, dormant twigs were collected from each tree species and kept in containers with water at room temperature. Emerged insects were collected and identified based on morphology and DNA barcoding of the mDNA COI region. Fungal DNA was extracted from pooled buds, twig parts and needles for species identification using a metabarcoding approach based on the rDNA ITS region. Here, we present preliminary results of this study and discuss them in the context of pest risk assessment.