Invasive alien species (IAS) are considered one of the greatest threats to biodiversity, particularly through their interactions with other drivers of change. Horizon scanning, the systematic examination of future potential threats and opportunities, leading to prioritization of IAS threats is seen as an essential component of IAS management. Our aim was to consider IAS that were likely to impact on native biodiversity but were not yet established in the wild in Great Britain. To achieve this, we developed an approach which coupled consensus methods (which have previously been used for collaboratively identifying priorities in other contexts) with rapid risk assessment. The process involved two distinct phases: Preliminary consultation with experts within five groups (plants, terrestrial invertebrates, freshwater invertebrates, vertebrates and marine species) to derive ranked lists of potential IAS.Consensus-building across expert groups to compile and rank the entire list of potential IAS.Five hundred and ninety-one species not native to Great Britain were considered. Ninety-three of these species were agreed to constitute at least a medium risk (based on score and consensus) with respect to them arriving, establishing and posing a threat to native biodiversity. The quagga mussel, Dreissena rostriformis bugensis, received maximum scores for risk of arrival, establishment and impact; following discussions the unanimous consensus was to rank it in the top position. A further 29 species were considered to constitute a high risk and were grouped according to their ranked risk. The remaining 63 species were considered as medium risk, and included in an unranked long list. The information collated through this novel extension of the consensus method for horizon scanning provides evidence for underpinning and prioritizing management both for the species and, perhaps more importantly, their pathways of arrival. Although our study focused on Great Britain, we suggest that the methods adopted are applicable globally.

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Summary1. Domestic gardens typically consist of a mixture of native and non-native plants which support biodiversity and provide valuable ecosystem services, particularly in urban environments. Many gardeners wish to encourage biodiversity by choosing appropriate plant taxa. The value of native and non-native plants in supporting animal biodiversity is, however, largely unknown. 2. The relative value of native and non-native garden plants to invertebrates was investigated in a replicated field experiment. Plots (deliberately akin to garden borders) were planted with one of three treatments, representing assemblages of plants based on origin (native, near-native and exotic). Invertebrates and resource measurements were recorded over four years. This paper reports the abundance of flower-visiting aerial insects ('pollinators') associated with the three plant assemblages. 3. For all pollinator groups on all treatments, greater floral resource resulted in an increase in visits. There was, however, a greater abundance of total pollinators recorded on native and near-native treatments compared with the exotic plots. Short-tongued bumblebees followed the same pattern whilst more hoverflies were recorded on the native treatment than the other treatments, and more honeybees on the near-native treatment. There was no difference between treatments in abundance of long-tongued bumblebees or solitary bees. The lack of difference in solitary bee abundance between treatments was probably due to a third of individuals from this group being recorded on one exotic plant species. 4. The number of flower visitors corresponded to the peak flowering period of the treatments, that is there were fewer flower visitors to the exotic treatment compared with the other treatments in early summer but relatively more later in the season. 5. Synthesis and applications. This experiment has demonstrated that utilizing plants from only a single region of origin (i.e. nativeness) may not be an optimal strategy for resource provision for pollinating insects in gardens. Gardens can be enhanced as a habitat by planting a variety of flowering plants, biased towards native and near-native species but with a selection of exotics to extend the flowering season and potentially provide resources for specialist groups.

The biology and pest status of Hylobius abietis Linnaeus in Europe are critically reviewed. New data are presented and the relationships between the weevil and its host plants considered. In Europe, H. abietis is the major pest of establishment forestry causing millions of ECUs of damage annually and perpetuating the addition of insecticide residues to sensitive habitats. Predator and parasitoid complexes in Britain and Europe are compared and contrasted. The lack of knowledge of the processes involved in adult dispersal and longevity are highlighted as major areas of concern. The biology and behaviour of the adult and larval stages are reviewed and new data presented. The feeding preferences of the adult weevils are considered and the possibility of using deterrents as a pest management strategy discussed. The development of risk assessment and forecasting tools aimed at more effective deployment of pest-management options are discussed. Risk criteria have their origins in important ecological relationships which require new understanding, but the prospects for determining high-risk forest sites are promising. The options for biological control are evaluated, in particular the use of mycopesticides and increased larval predation. It is concluded that much more research into the biology and ecology of H. abietis is required before a successful Integrated Pest Management (IPM) programme can be initiated.

Citizen science is an increasingly popular way of engaging volunteers in the collection of scientific data. Despite this, data quality remains a concern and there is little published evidence about the accuracy of records generated by citizen scientists. Here we compare data generated by two British citizen science projects, Blooms for Bees and BeeWatch, to determine the ability of volunteer recorders to identify bumblebee ( Bombus ) species. We assessed recorders’ identification ability in two ways–as recorder accuracy (the proportion of expert-verified records correctly identified by recorders) and recorder success (the proportion of recorder-submitted identifications confirmed correct by verifiers). Recorder identification ability was low (<50% accuracy; <60% success), despite access to project specific bumblebee identification materials. Identification ability varied significantly depending on bumblebee species, with recorders most able to correctly identify species with distinct appearances. Blooms for Bees recorders (largely recruited from the gardening community) were markedly less able to identify bumblebees than BeeWatch recorders (largely individuals with a more specific interest in bumblebees). Within both projects, recorders demonstrated an improvement in identification ability over time. Here we demonstrate and quantify the essential role of expert verification within citizen science projects, and highlight where resources could be strengthened to improve recorder ability.