insects Review Beyond the Decline of Wild Bees: Optimizing Conservation Measures and Bringing Together the Actors Maxime Drossart * and Maxence Gérard * Laboratory of Zoology, Research Institute for Biosciences, University of Mons (UMONS), Place du Parc 20, B-7000 Mons, Belgium * Correspondence: [email protected] (M.D.); [email protected] (M.G.) Received: 3 September 2020; Accepted: 18 September 2020; Published: 22 September 2020 Simple Summary: Wild bees represent the main group of pollinators in Europe, being responsible for the reproduction of numerous flowering plants. However, like a non-negligible part of biodiversity, this group has been facing a global decline mostly induced by numerous human factors over the last decades. Overall, even if all the questions are not solved concerning the causes of their decline, we are beyond the precautionary principle because the decline factors are roughly known, identified and at least partially quantified. Experts are now calling for effective actions to promote wild bee diversity and the enhancement of environmental quality. In this review, we present a general and up-to-date assessment of the conservation methods, as well as their efficiency and the current projects that try to fill the gaps and optimize the conservation measures. This publication aims to be a needed catalyst to implement concrete and qualitative conservation actions for wild bees. Abstract: Wild bees are facing a global decline mostly induced by numerous human factors for the last decades. In parallel, public interest for their conservation increased considerably, namely through numerous scientific studies relayed in the media. In spite of this broad interest, a lack of knowledge and understanding of the subject is blatant and reveals a gap between awareness and understanding. While their decline is extensively studied, information on conservation measures is often scattered in the literature. We are now beyond the precautionary principle and experts are calling for effective actions to promote wild bee diversity and the enhancement of environment quality. In this review, we draw a general and up-to-date assessment of the conservation methods, as well as their efficiency and the current projects that try to fill the gaps and optimize the conservation measures. Targeting bees, we focused our attention on (i) the protection and restoration of wild bee habitats, (ii) the conservation measures in anthropogenic habitats, (iii) the implementation of human made tools, (iv) how to deal with invasive alien species, and finally (v) how to communicate efficiently and accurately. This review can be considered as a needed catalyst to implement concrete and qualitative conversation actions for bees. Keywords: wild bees; insect pollinator; decline; conservation actions; conservation tools 1. Introduction Over the last decade, public interest in the conservation of pollinators increased considerably, thanks in particular to numerous scientific studies relayed in the media [1–3]. While some less-charismatic insect taxa remain unknown from public appreciation [4], marketing pollinator conservation is an easier sell to a broad audience. However, while this interest seems to be already acquired for a majority of the population, a lack of knowledge and understanding of the subject is Insects 2020, 11, 649; doi:10.3390/insects11090649 www.mdpi.com/journal/insects Insects 2020, 11, 649 2 of 23 blatant and thus reveals a gap between awareness and understanding [2]. This gap is particularly characterizedInsects 2020, 11 by, x FOR a general PEER REVIEW lack of awareness of the great diversity of pollinators (e.g., bees,2 hoverflies, of 23 butterfliesacquired::: for). a For majority example, of the respectively population, 80% a lack and of 99% knowledge of survey and respondents understanding in Greatof the Britainsubject is and the Unitedblatant States and claim thus reveals that bees a gap are between important, awareness but only and 3% understanding and 14% can [2]. assess This gap the is number particularly of species foundcharacterized in their country by a general [2,5]. lack Moreover, of awareness most of citizens the great are diversity able to of identify pollinators honeybees (e.g., bees, and hoverflies, bumblebees as beebutterflies…). species, but For the example, other wildrespectively bee species 80% and are 99 poorly% of survey recognized respondents as bees in Great [2]. 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Such a lack of knowledge could therefore lead, on the basis of good of pollination, but not the phenomenon and its magnitude as a whole (e.g., the importance of intentions,combining to irrelevant floral resources actions, and misguided, nesting sites, or the even existence counterproductive of different major measures groups for of thepollinators protection of threatenedwith sometimes pollinator specific species requiremen [2]. Thets, misinterpretation etc.). Such a lack of of knowledge scientific articles, could therefore sometimes lead, amplified on the by media,basis can of good even intentions, accentuate to these irrelevant inappropriate actions, misguided, actions. or Clearly, even counterproductive the awareness of measures public audiencefor has notthe grownprotection with of thethreatened increase pollinator of scientific species research [2]. onThe this misinterpretation topic. Yet for scientists,of scientific identifying articles, and prioritizingsometimes threatened amplified populations by media, can is challenging even accentua andte stillthese subject inappropriate to ongoing actions. investigation Clearly, the [6]. As a basisawareness for all researchers, of public audience Harvey has and not colleagues,grown with the [7] increase formulated of scientific an informative research on road this maptopic. forYet insect conservationfor scientists, and identifying recovery. and prioritizing threatened populations is challenging and still subject to ongoing investigation [6]. As a basis for all researchers, Harvey and colleagues, [7] formulated an Overall, the abundance of terrestrial insects has indeed deceased by 9% per decade and the wild informative road map for insect conservation and recovery. bees are not an exception to the rule [8]. Literature about the deleterious impact of stressors on wild Overall, the abundance of terrestrial insects has indeed deceased by 9% per decade and the wild beesbees is abundant are not an [9 exception,10]. To slow to the down rule [8]. their Literature negative about impacts, the deleterious the development impact of of stressors national on and wild regional initiativesbees is hasabundant been more[9,10] and. To moreslow down associated their withnegative the impacts, implementation the development of restoration of national and protectionand actionsregional for pollinators initiatives has for been the lastmore few and years. more Allasso ofciated these with conservation the implementa actionstion undertakenof restoration locally and are of paramountprotection actions importance for pollinators in the preservation for the last few of ye localars. All biodiversity. of these conservation Indeed, whileactions many undertaken species are threatenedlocally are on of a localparamount scale andimportance even su inff erthe regional preservation extinction, of local theybiodiversity. may still Indeed, remain while quite many common withinspecies their are overall threatened geographical on a local scale range and [3 ,even11,12 suff]. Thiser regional phenomenon extinction, can they be may observed still remain for instance quite by comparingcommon global within (e.g., their Europeanoverall geographical scale) and range regional [3,11,12]. IUCN This Red phenomenon Lists [13]. As can an be example, observed many for bee instance by comparing global (e.g., European scale) and regional IUCN Red Lists [13]. As an example, species from Belgium are (nearly) threatened or even extinct at a regional scale while their populations many bee species from Belgium are (nearly) threatened or even extinct at a regional scale while their are not preoccupying at European scale (i.e., LC, Least Concern) [14,15] (Figure1). This paradox populations are not preoccupying at European scale (i.e., LC, Least Concern) [14,15] (Figure 1). This highlightsparadox the highlights importance the importance of conservation of conservati measureson measures at various at various geographical geographical scales. scales. (A) (B) FigureFigure 1. 1.IUCN IUCN Red List List status status in ( inA) (EuropeA) Europe [14] and [14 (]B and) Belgium (B) Belgium[15]. The proportion [15]. The of proportion (nearly) of threatened