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As the number of observations submitted to the citizen science platform iNaturalist continues to grow, it is increasingly important that these observations can be identified to the finest taxonomic level, maximizing their value for biodiversity research. Here, we explore the benefits of acting as an identifier on iNaturalist.

The Wallacean shortfall—lack of adequate knowledge of a species’ distribution in the geographic space—hinders practical actions towards species conservation, and such severe data deficit is ubiquitous when dealing with insect species. Considering the effects of human activities on Earth, especially in the last 50 years, proper delimitation of species distributions is of utmost importance for their conservation, but this is challenging when occurrence data for a species are limited. Here, we present suitable areas of occurrence for a recently-described specialist bee in the Southeastern United States (Colletes ultravalidus Hall and Ascher), modeled with presence-only methods that are robust to small number of occurrence points. Incorporation of new citizen science data points derived from images submitted online for identification enhanced the species distribution model which, in turn, validated the new sites as suitable for the species. Consideration of absence points, i.e. sites where the species was not recorded despite intensive surveys for Colletes and other specialist bees, resulted in more precise predications that can inform future searches for this bee. This study exemplifies how citizen-science projects may contribute to improving understanding of species biogeographic ranges and thus to overcoming the Wallacean shortfall. The need for critical evaluation prior to and after modeling of the occurrences obtained by non-specialists are discussed.

The article was funded by the “CUT Open Access Author Fund” Cyprus, the third largest island in the Mediterranean, constitutes a biodiversity hotspot with high rates of plant endemism. The wild bees of the island were studied extensively by the native George Mavromoustakis, a world-renowned bee taxonomist, who collected extensively on the island from 1916 to 1957 and summarised his results in a series of eight Cyprus-specific papers published from 1949 ["1948"] to 1957. The current work represents the first modern checklist of the wild bees of Cyprus, based on a compilation of previous publications, museum specimens and authors' recent collections. Overall, 369 verified wild bee species have been recorded on the island, with eleven species reported from Cyprus for the first time. The island hosts all six of the globally widespread bee families, with Apidae represented by 110 species, Megachilidae with 91, Andrenidae with 76, Halictidae with 72, Colletidae with 19, and Melittidae with 1. Twenty-one of the recorded bee species are endemic (i.e., 5.7 % endemism rate) and Cyprus ranks third after Lesvos and Sicily in known bee species richness among the Mediterranean islands. Previously unpublished records from various locations on Cyprus for 156 previously reported bee species are also provided in the study. The current work provides a baseline for future studies of wild bee diversity on the island of Cyprus and neighbouring regions.

We determined the bee species presence, abundance, and diversity at utility-scale ground-mounted solar development (USS) to assess the impact on desert pollinators and the services they provide to the plants in the communities in which they live, specifically, in the Mojave and Colorado Desert regions. We used a matched transect control design to test whether pollinator populations have changed due to solar utility scale installations. Sixty to 90% of flowering plants require animal pollinators. The Mojave Desert represents a hotspot of bee biodiversity corresponding to its rich botanical diversity of 1512 species. Our study found 113 species in a severe drought year after five drought years (2011-2015). 42% were oligoleges, 10% were polylectic and 29% of the lacked data on their floral diets. Included were 5 undescribed species in the families Apidae (Tetraloniella, Anthophora -Anthophoroides, Anthophorula,) and Halictidae (Lasioglossum [Dialictus]). In our transect study we found lower abundance, diversity and richness inside the solar installations. However, we did not find a significant effect of distance from solar installation at 2K for our one year study. The BVT traps represented 16% of the collected specimens and 58 species and cup traps represented 83% of traps, and captured 46.7% of the total specimens and 66 species.Of the total bees species captured and identified, 76% are ground-nesting species.

Table S1. List of major sites surveyed for bees and their habitat classification.

Traditional conservation techniques for mapping highly biodiverse areas assume there to be satisfactory knowledge about the geographic distribution of biodiversity. There are, however, large gaps in biological sampling and hence knowledge shortfalls. This problem is even more pronounced in the tropics. Indeed, the use of only a few taxonomic groups or environmental surrogates for modelling biodiversity is not viable in mega-diverse countries, such as Brazil. To overcome these limitations, we developed a comprehensive spatial model that includes phylogenetic information and other several biodiversity dimensions aimed at mapping areas with high relevance for biodiversity conservation. Our model applies a genetic algorithm tool for identifying the smallest possible region within a unique biota that contains the most number of species and phylogenetic diversity, as well as the highest endemicity and phylogenetic endemism. The model successfully pinpoints small highly biodiverse areas alongside regions with knowledge shortfalls where further sampling should be conducted. Our results suggest that conservation strategies should consider several taxonomic groups, the multiple dimensions of biodiversity, and associated sampling uncertainties.

Resin bees of the subgenus Ranthidiellum, are rare and endemic to Southeast Asia. These bees are known to construct resinous entrance tubes to their nests. Here, the new species Anthidiellum (R.) phuchongensissp. nov.is described along with a description of its nest collected from Phu Chong Na Yoy National Park, Ubon Ratchathani Province, Thailand. In addition, the bee cleptoparasite, Stelis (Malanthidium) flavofuscinularsp. nov., and the male of A. (R.) ignotum Engel, 2009, are described for the first time. A key toRanthidiellumspecies is also provided.

Morocco is a well known hot-spot of biodiversity in the Mediterranean basin. While some taxa like vascular plants are relatively well recorded, important groups of pollinators like bees are still understudied. This article presents an updated checklist of the bee species of Morocco and includes a summary of global and regional distribution of each species. A total of 961 species belonging to six bee families and 68 genera are recorded: Andrenidae (8 genera, 217 species); Apidae (15 genera, 241 species); Colletidae (2 genera, 74 species), Halictidae (12 genera, 144 species), Megachilidae (28 genera, 271 species) and Melittidae (3 genera, 14 species). Among them, 67 species are recorded for the first time in Morocco. Around 70% of the bee fauna of Morocco consists of widespread Palaearctic species. Only 18% of Moroccan species recorded are restricted to North Africa and 8% are Moroccan single-country endemics (81 species). Afrotropical elements in the Moroccan fauna are few, with only 3% of Morocco species co-occuring in that region. This checklist is intended to stimulate new regional research on bees including their taxonomy and biogeography. As many groups of bees have been understudied, discovery of new species for science and new records for the country can be expected. Additional research including inventorying, monitoring, and integrative taxonomic studies are needed to develop a comprehensive strategy for bee conservation in Morocco.

The Chinese bees of the genus Anthidium Fabricius, 1804, are reviewed. Twenty-one species are confirmed to occur in China, five of which are described and illustrated as new Chinese endemics: Anthidium (Anthidium) pseudomontanum Niu & Zhu, sp. nov., A. (A.) pseudophilorum Niu & Zhu, sp. nov., A. (A.) tasitiense Niu & Zhu, sp. nov., A. (A.) xuezhongi Niu & Zhu, sp. nov., and A. (Proanthidium) qingtaoi Niu & Zhu, sp. nov.. The previously unknown female of A. (A.) kashmirense Mavromoustakis, 1937 and male of A. (P.) kashgarense (Cockerell, 1911) are described for the first time. Anthidium (A.) furcatum Wu, 2004 (junior primary homonym, nec Anthidium furcatum Ducke, 1908) is replaced with its valid and available synonym A. (A.) striatum Wu, 2004. New synonymies are also established for A. (A.) kashmirense Mavromoustakis, 1937 = A. (A.) nigroventrale Wu, 1982, syn. nov., and A. (A.) florentinum (Fabricius, 1775) = A. (A.) helianthinum Wu, 2004, syn. nov. The non-Chinese Anthidium amabile Alfken, 1933 (junior primary homonym, nec Anthidium porterae var. amabile Cockerell, 1904) is unavailable and the available name Anthidium (Proanthidium) minimum Pasteels, 1969, is valid for this species. Updated synonymies and distributional data are provided for some widespread Palaearctic species including two now adventive in the New World. For Chinese species, the distribution and floral associations of each are provided along with illustrations and a key to the known species.

Resin bees of the subgenus Ranthidiellum, are rare and endemic to Southeast Asia. These bees are known to construct resinous entrance tubes to their nests. Here, the new species Anthidiellum (R.) phuchongensissp. nov. is described along with a description of its nest collected from Phu Chong Na Yoy National Park, Ubon Ratchathani Province, Thailand. In addition, the bee cleptoparasite, Stelis (Malanthidium) flavofuscinularsp. nov., and the male of A. (R.) ignotum Engel, 2009, are described for the first time. A key to Ranthidiellum species is also provided.

Five Chinese species of Nomia (Gnathonomia) Pauly, 2005 are treated in this paper: Nomia fusciventris Zhang & Niu, sp. nov. from Fujian Province is described as a new species; N. aurata Bingham, 1897 and N. wahisi Pauly, 2009 are recorded from China for the first time, and the male of N. pieli Cockerell, 1931 is newly reported. An updated diagnosis is provided for the subgenus Nomia (Gnathonomia) to accommodate Chinese endemic species which lack the white integumental bands found in most previously described forms. A key to the known Chinese species is provided.

Large aggregations of solitary bees have been reported from natural and managed landscapes where abundant nesting habitat and floral resources co-occur. Here we describe an unusually large aggregation of the bee Anthophora (Melea) bomboides Kirby, 1838 (Hymenoptera: Apidae) nesting in a coastal bluff in San Juan County, Washington State. Nest densities as high as 630/m2 were recorded along a steep sandy embankment measuring 1.0 km long with a mean height of 9.3 m. The population estimate of 133,492 nesting females exceeds previously reported occurrences for this species by two orders of magnitude. Floral resources supporting this aggregation over three years of observation included dense flowering shrubs covering 16 ha of abandoned farmland immediately adjacent to the bluff. We also report an additional 31 species of bees and wasps collected at the site and discuss recently adopted conservation measures to protect the site's floral resources from conifer encroachment.

More than 120 native bee species have been documented in Maine since 1930 in association with the native plant Vaccinium angustifolium (Lowbush Blueberry). We report 3 studies in commercial Lowbush Blueberry fields: (1) a survey of diversity in Osmia (mason bees) and closely related Megachile (leaf-cutter bees) using trap nests in 93 fields from 1990 to 2012, (2) a 29-year study of a native bee community, and (3) an examination of climate-change effects on bee-foraging periods during blueberry bloom. Osmia appeared to be more stable over a 22- year period in their species richness and relative abundances in Lowbush Blueberry fields when compared to Megachile over a similar 17-year period. The native bee community in a single location in Winterport was observed to fluctuate in abundance 2 to 3 times annually. Modeling of the total bee community and taxa-specific group abundances (Bombus, Megachilids, Andrenids, and Halictids and other bees) suggest that while stochastic density-independent processes such as weather can play a role in determining their annual oscillations, density-dependent lags of 1 and 2 years appear to be the main driving forces. Estimation of fruit set over the same 29-year period, based upon native bee abundance, suggests that pollination is more buffered than community bee abundance, resulting in a lesser degree of fluctuation over time. We speculate that this finding is due to redundancy in floral preferences, multiple floral visitations, and differing pollination efficiencies by the highly diverse native bee community associated with Lowbush Blueberry. Effects of climate change in Maine Lowbush Blueberry fields during May bloom was investigated using a historic weather database. Since the early 1990s, precipitation has, to a large degree, reduced the number of optimal bee foraging days during bloom, with implications for pollination and bee species abundances. This new information reinforces the need for provision of pollinator gardens to support native pollinators of Lowbush Blueberry.

We present a new county checklist developed from bee research in Maine since the 1800s. The list contains 278 bee species in 37 genera and 6 families, of which all but 8 are native, with ≥50 taxa each in Andrena and Lasioglossum. Data for 16 counties from publications, museum collections, and recent surveys varied in number of species from 8 (Androscoggin) to 197 (Hancock). Research since 1930 on Vaccinium angustifolium (Lowbush Blueberry) led to many records. Twenty-one species are considered unusual, including 3 first recorded in 2016: Epeoloides pilosulus, Melitta melittoides, and Holcopasites calliopsidis. Maine records provide evidence of declines in Bombus affinis, decline in B. terricola followed by partial recovery, and increase in B. impatiens. Crops that should be studied regarding associated bees are Malus pumila (Apple), Vaccinium corymbosum (Highbush Blueberry), Vaccinium macrocarpon (American Cranberry), and Curcurbitaceae (cucurbits). Montane, sandy, and island habitats were identified as priorities for future sampling. We discuss records of bee species from New England relevant to understanding the Maine fauna, bee diversity, changes in abundance, cleptoparasitism, pesticide impacts, habitat requirements, and climate change.

A new species of the panurgine bee genus Mermiglossa Friese (Panurginae) is described and figured from females captured near Voi in the southern part of the former Coast Province, Kenya, a historical type locality for several bee species. Mermiglossa voicola Ascher & Engel, new species, is distinguished from the only other species of the genus, M. rufa Friese from central Namibia. The new species is readily identified due to its black rather than red metasoma and compound eyes slightly convergent above rather than parallel-sided. The new species raises the total number of described bee species for Kenya to 343, extends the known distribution of its genus and subtribe from the Namib Desert of southwestern Africa to the western edge of the Nviri Desert of East Africa, and provides further evidence of extensive biogeographic connections between these disjunct xeric areas. Recent changes in the family-group classification of Old World Panurginae are discussed in relation to recognition of Mermiglossina as a valid subtribe within an expanded tribe Panurgini also including the New World perditines.

Reports of world-wide decline of pollinators, and of bees in particular, raise increasing concerns about maintenance of pollination interactions. While local factors of bee decline are relatively well known and potential mitigation strategies at the landscape scale have been outlined, the regional and continental-scale threats to bee diversity have only been marginally explored. Here we document large-scale spatial patterns for a representative bee subfamily, the determinants of its species richness, and assess major threats to these pollinators. Using a comprehensive global dataset of Colletinae (genera Colletes, also called “polyester” or “cellophane” bees for their underground nests lined with a polyester secretion, and Mourecotelles), a species-rich subfamily whose organismal and physiological ecology is representative of many bees, we measured species richness and endemism on global to continental scales. We explored the relationships between bee species richness and potential environmental stress factors grouped into three categories: contemporary climate, habitat heterogeneity, and anthropogenic pressure. Bees of the subfamily Colletinae demonstrate the reversed latitudinal gradient in species richness and endemism suggested for bees; the highest species richness of Colletinae was found between 30° and 50° latitude in both the northern and southern hemispheres. Centres of endemism largely overlapped with those of species richness. The importance of the Greater Cape Floristic Region, previously identified as a centre of richness and endemism of bees, was confirmed for Colletinae. On the global scale, present-day climate was a significant predictor of species richness as was flowering plant diversity represented by vascular plant species richness and centres of plant diversity. Our main conclusion is that climate change constitutes a potential threat to bee diversity, as does declining diversity of vascular plants. However, a significant overlap between centres of bee richness and plant diversity might increase chances for developing conservation strategies.

The science of taxonomy faces many challenges at present. Many questions remain as to how we can best continue the vital practice of describing and understanding biodiversity. Here, we discuss how best to modernize taxonomy, how we might improve taxonomy in developing countries, and how taxonomists can better interface with other fields to better science as a whole.

International audience; Species invasions are expected to increase continuously with undeniable impact upon native biodiversity, being an important process in relation to the decline of native pollinators. We used species distribution models and multivariate analyses to assess the climatic niche properties of the red dwarf honey bee, Apis florea Fabricius (Apidae: Apini), an open-nesting species native to southern Asia and parts of the Middle East, currently invading East Africa, Sundaic tropical Southeast Asia (Peninsular Malaysia and Singapore), and East Asia (Taiwan). The species’ niche was relatively conserved, with the climatic conditions in all its invaded range overlapped by those from its native one. Its potential distribution in Africa and the Indomalayan region is broad, with anthropogenic areas likely providing new habitats and dispersal corridors in areas that were formerly too arid or too heavily forested to allow its dispersal. Future studies to evaluate the potential impacts of A. florea in invaded ranges are encouraged.

The Chinese bees of the genus Trachusa Panzer, 1804 are reviewed. Nine species are confirmed to occur in China. Three new species are described and illustrated: Trachusa (Paraanthidium) pingdaensis Niu, sp. nov., T. (P.) staabi Niu, sp. nov. and T. (P.) wuae Niu, sp. nov. The distribution of each species is given. An illustrated key to the Chinese species is provided.

This revision of the bee genus Bathanthidium Mavromoustakis, 1953, treats 12 species, with 11 recorded from China, including Bathanthidium fengkaiense Niu & Zhu, sp. nov.. Two species are proposed as new combinations in genus Bathanthidium: Anthidium (s. str.) bicolor Wu, 2004, A. (s. str.) monganshanensis Wu, 2004. The two new combinations (B. bicolor, B. monganshanense) are in Bathanthidium (Manthidium), previously considered to include only the type species from Burma and Laos (published records from northeastern India and Malaysia are based on misinterpreted localities). Trachusa (Paraanthidium) concavum (Wu, 1962) and Stelis siamensis Friese, 1925 are synonymized with B. binghami (Friese, 1901). Bathanthidium circinatum Wu, 2004 is transferred to Pseudoanthidium Friese forming the new combination P. (s. str.) circinatum (Wu, 2004). The distribution of each species is given, new distribution sites are marked by asterisk (*) especially. Our results confirm that the genus Bathanthidium has higher species diversity than previously documented and that this diversity is centered in China.

We document a novel exotic bee for North America,Hylaeus(Hylaeus)communisNylander, 1852 (Hymenoptera: Colletidae), and determine whether it is likely to spread widely across the continent. To evaluate the extent to whichH. communisbehaves as a generalist and would be able to adapt to novel North American environments, we compare the breadth of its climatic, floral, habitat, and nesting preferences between its native European range and sites where it was first discovered in southern Québec, Canada. Specifically, we calculate the paired difference index, which approximates species generalism, from a set of bipartite networks linkingHylaeusFabricius, 1793 species to their respective floral hosts and habitats. Results indicate thatH. communisis the most adaptable bee of the EuropeanHylaeusfauna and will likely acclimate to its new environment, being a greater generalist than an already widely established exotic bee,H. hyalinatusSmith, 1842. In southern Québec, we find that, despite visiting a wide variety of flowering species, it exhibits a strong association with non-native plants and resides almost exclusively in urban settings. We hypothesise thatH. communiswill be able to spread widely throughout North America via multiple human-mediated but accidental dispersal events and by following the distribution of European weeds and horticultural plants.

AimThe knowledge of biodiversity facets such as species composition, distribu-tion and ecological niche is fundamental for the construction of biogeographichypotheses and conservation strategies. However, the knowledge on these facetsis affected by major shortfalls, which are even more pronounced in the tropics.This study aims to evaluate the effect of sampling bias and variation in collec-tion effort on Linnean, Wallacean and Hutchinsonian shortfalls and diversitymeasures as species richness, endemism and beta-diversity.LocationBrazil.MethodsWe have built a database with over 1.5 million records of arthro-pods, vertebrates and angiosperms of Brazil, based on specimens deposited inscientific collections and on the taxonomic literature. We used null models totest the collection bias regarding the proximity to access routes. We also testedthe influence of sampling effort on diversity measures by regression models. Toinvestigate the Wallacean shortfall, we modelled the geographic distribution ofover 4000 species and compared their observed distribution with models. Toquantify the Hutchinsonian shortfall, we used environmental Euclidean distanceof the records to identify regions with poorly sampled environmental condi-tions. To estimate the Linnean shortfall, we measured the similarity of speciescomposition between regions close to and far from access routes.ResultsWe demonstrated that despite the differences in sampling effort, thestrong collection bias affects all taxonomic groups equally, generating a patternof spatially biased sampling effort. This collection pattern contributes greatly tothe biodiversity knowledge shortfalls, which directly affects the knowledge onthe distribution patterns of diversity.Main conclusionsThe knowledge on species richness, species composition andendemism in the Brazilian biodiversity is strongly biased spatially. Despite dif-ferences in sampling effort for each taxonomic group, roadside bias affectedthem equally. Species composition similarity decreased with the distance fromaccess routes, suggesting collection surveys at sites far from roads couldincrease the probability of sampling new geographic records or new species. ObjetivoO conhecimento das facetas da biodiversidade como composição, distribuição e nicho ecológico das espécies é fundamental para a construção de hipóteses biogeográficas e estratégias de conservação. No entanto, o conhecimento sobre essas facetas é afetado por grandes déficits, que são ainda mais pronunciados nos trópicos. Este estudo visa avaliar o efeito do viés de amostragem e variação no esforço de coleta sobre os déficits e medidas de diversidade de Linnean, Wallacean e Hutchinsonian como riqueza de espécies , endemismo e beta-diversidade.LocalizaçãoBrasil.MétodosConstruímos um banco de dados com mais de 1,5 milhão de registros de artrópodes, vertebrados e angiospermas do Brasil, com base em espécimes depositados em coleções científicas e na literatura taxonômica. Utilizamos modelos nulos para testar o viés de coleta quanto à proximidade das vias de acesso. Também testamos a influência do esforço amostral nas medidas de diversidade por meio de modelos de regressão. Para investigar o déficit Wallaceano, modelamos a distribuição geográfica de mais de 4.000 espécies e comparamos sua distribuição observada com modelos. Para quantificar o déficit hutchinsoniano, utilizamos a distância euclidiana ambiental dos registros para identificar regiões com condições ambientais pouco amostradas. Para estimar o déficit de Linne, medimos a similaridade da composição de espécies entre regiões próximas e distantes das vias de acesso. Resultados Demonstramos que apesar das diferenças no esforço amostral, o forte viés de coleta afeta igualmente todos os grupos taxonômicos, gerando um padrão de esforço amostral enviesado espacialmente. Esse padrão de coleta contribui muito para as deficiências de conhecimento da biodiversidade, o que afeta diretamente o conhecimento sobre os padrões de distribuição da diversidade.Principais conclusõesO conhecimento sobre riqueza de espécies, composição de espécies e endemismo na biodiversidade brasileira é fortemente enviesado espacialmente. Apesar das diferenças no esforço amostral para cada grupo taxonômico, o viés de beira de estrada os afetou igualmente. A similaridade da composição de espécies diminuiu com a distância das vias de acesso, sugerindo que levantamentos de coleta em locais distantes de estradas podem aumentar a probabilidade de amostragem de novos registros geográficos ou novas espécies.

Mature larvae of five species representing each of the three principal groups within the genus Megachile sensu lato (i.e., including Creightonella and Chalicodoma, which are often recognized at generic rank) are described and are revealed to be quite similar to one another. On the basis of their descriptions a larval description of the genus is formulated. This, in turn, is compared with and found quite similar to a previously published Preliminary Description of Mature Larvae of the Megachilini based on study of larval representatives of the three genera in the tribe: Megachile, all species of which are pollen-collecting, and Coelioxys and Radoszkowskiana, both of which are cleptoparasitic, usually with Megachile hosts.

We report and annotate new Connecticut state records for fourteen bee species: Eucera (Synhalonia) hamata (Bradley), Holcopasites calliopsidis calliopsidis (Linsley), Nomada tiftonensis Cockerell, Triepeolus remigatus (Fabricius), Andrena (Derandrema) uvulariae Mitchell, Pseudopanurgus compositarum (Robertson), Lasioglossum (Dialictus) abanci (Crawford), Lasioglossum (Dialictus) lionotum (Sandhouse), Lasioglossum (Dialictus) michiganense (Mitchell), Lasioglossum (Dialictus) platyparium (Robertson), Lasioglossum zonulum (Smith), Hylaeus (Prosopis) illinoisensis (Robertson), Hylaeus (Prosopis) aff. nelumbonis, and Hylaeus (Prosopis) schwarzii (Cockerell). In addition, we report and discuss other noteworthy bee records from Connecticut to clarify taxonomy, nomenclature, status, habitat, or ecoregion.

Summary Insects are the focus of many recent studies suggesting population declines, but even invaluable pollination service providers such as bees lack a modern distributional synthesis. Here, we combine a uniquely comprehensive checklist of bee species distributions and >5,800,000 public bee occurrence records to describe global patterns of bee biodiversity. Publicly accessible records are sparse, especially from developing countries, and are frequently inaccurate throughout much of the world, consequently suggesting different biodiversity patterns from checklist data. Global analyses reveal hotspots of species richness, together generating a rare bimodal latitudinal richness gradient, and further analyses suggest that xeric areas, solar radiation, and non-forest plant productivity are among the most important global drivers of bee biodiversity. Together, our results provide a new baseline and best practices for studies on bees and other understudied invertebrates.

Southeast (SE) Asia holds high regional biodiversity and endemism levels but is also one of the world's most threatened regions. Local, regional and global threats could have severe consequences for the future survival of many species and the provision of ecosystem services. In the face of myriad pressing environmental problems, we carried out a research prioritisation exercise involving 64 experts whose research relates to conservation biology and sustainability in SE Asia. Experts proposed the most pressing research questions which, if answered, would advance the goals of biodiversity conservation and sustainable development in SE Asia. We received a total of 333 questions through three rounds of elicitation, ranked them (by votes) following a workshop and grouped them into themes. The top 100 questions depict SE Asia as a region where strong pressures on biodiversity interact in complex and poorly understood ways. They point to a lack of information about multiple facets of the environment, while exposing the many threats to biodiversity and human wellbeing. The themes that emerged indicate the need to evaluate specific drivers of biodiversity loss (wildlife harvesting, agricultural expansion, climate change, infrastructure development, pollution) and even to identify which species and habitats are most at risk. They also suggest the need to study the effectiveness of practice-based solutions (protected areas, ecological restoration), the human dimension (social interventions, organisational systems and processes and, the impacts of biodiversity loss and conservation interventions on people). Finally, they highlight gaps in fundamental knowledge of ecosystem function. These 100 questions should help prioritise and coordinate research, conservation, education and outreach activities and the distribution of scarce conservation resources in SE Asia. Accepted version The workshop was funded by a generous donation from Haiyi Holdings Pte Ltd. to the Department of Biological Sciences of the National University of Singapore.