An identification key based on French ladybird colouration is proposed for the tribes Chilocorini, Coccinellini, and Epilachnini. These tribes were chosen based on their relatively limited species diversity, as well as their large size and high colour diversity, making them easy to observe and collect. The identification key runs on Xper³ software, which allows the building of structured knowledge bases and online free-access keys. The online interactive Xper key is available at http://french-ladybird.identificationkey.fr.

Citizen science, Coccinellidae , Coccinellini , Chilocorini , Epilachnini , France, interactive identification keys, ladybirds, Xper

The identification of species is central in ecology, conservation biology, systematics, and related disciplines (species inventories and community studies, ecosystem management, establishment and improvement of environmental public policies, taxonomic reviews, and management of natural history collections) (Oliver 1988, Hebert et al. 2003, Smith et al. 2008, Vander Zanden et al. 2010). Europe is one of the best-known parts in the world in terms of biodiversity (Fontaine et al. 2012), especially concerning distribution patterns at the country scale. This has been highlighted by the release of the Fauna Europaea database since 2004 (de Jong et al. 2014), which gathers the scientific names and distributions of all living European animal species and is assembled by a large network of specialists. However, most new species are described by non-professional taxonomists (Fontaine et al. 2012) and the distribution of a majority of organisms remains poorly known. Citizen science programs aim to fill that gap (Silvertown 2009), thanks to the participation of amateurs and the general public to the inventory and description of life (e.g., National Biodiversity Network in the UK, Swedish Species Gateway in Sweden, Chicago Wilderness Project in the USA, Vigie-Nature in France; see Silvertown 2009). From this perspective, visual and interactive identification of species offers tremendous potential for the general public.

If the identification of large and charismatic animals may be easy, the majority of organisms require expert skills for accurate identification and the inability to identify species represents a major challenge known as the Taxonomic Impediment (SCBD 2010). The most basic requirement for people studying and working on biodiversity aspects is the availability of species identification guides. However, easy-to-use identification guides for non-taxonomists and the general public are scarce and available for relatively few taxonomic groups (SCBD 2010). Consequently, the other features of organisms (such as distribution, ecology, biology) remain poorly known (Costello et al. 2006, SCBD 2010).

Coccinellidae is a family of beetles popular and appreciated by naturalists and the general public. Because these animals have ecological and economic values as predators of pest insects (e.g. aphids, scale insects), their identification may be of importance for naturalists, amateurs and professionals (Hemptinne et al. 2005, Hodek and Honěk 2009, Ali et al. 2014). Several citizen science programs aim to describe the distribution patterns of this group: we can mention for instance the Harlequin Ladybird Survey (http://www.harlequin-survey.org) and the Ladybird Survey (http://www.ladybird-survey.org) in the UK, the Lost Ladybug Project (http://www.lostladybug.org) and the Buckeye Lady Beetle Blitz (https://entomology.osu.edu/about-us/multimedia/buckeye-lady-beetle-blitz) in the US, and the Coccinula Recording Scheme in Belgium (Baugnée et al. 2011). The data collected led to a significant number of scientific works that have been published (e.g., Brown et al. 2008, Comont et al. 2012, 2014, Gardiner et al. 2012, Purse et al. 2015).

Single-access identification keys consist of a series of identification steps that form a single and unique identification path for a given taxon. Although it is a very powerful tool for identifying species, the user cannot choose the character to be observed (the answer for every single step must be known), and the identification is impossible if some characters are missing (e.g., if the specimen is poorly preserved). Moreover, this type of keys cannot be modulated or adapted to various kinds of publics, environmental conditions, season, or geographical location.

Most North American or European ladybird identification keys are single-access and difficult to use for non-specialists (Dauguet 1949, Iablokoff-Khnzorian 1982, Gordon 1985, Chapin and Brou 1991). Others are mainly based on shape and colour, but most characters need specific vocabulary, which makes the key still too complicated for the general public in the perspective of citizen science programs (Belgium: Baugnée and Branquart 2000; West of France: Le Monnier and Livory 2003; British Isles: Roy et al. 2013; North of France: Declercq et al. 2014).

Modern tools developed along with digital technologies and data processing make identification easier for the user. In this perspective, several interactive identification keys (IIK) are available online (e.g., http://www.ladybird-survey.org/bbc/spotter.php, http://www.discoverlife.org/20/q?guide=Ladybug), but most of them are only digital versions of single-access keys and maintain the same difficulties for the user.

A multi-access interactive key is a computer-aided identification tool that makes it possible to find correct names of species where the user enters attributes (character-state values) of the specimen (Dallwitz et al. 2013). The advantages compared to conventional keys are as follows: characters can be used in any order, characters are ordered to start with the one that best separates the remaining taxa, keys can be completed with illustrations (pictures, drawings) and texts explaining the terminology used, correct identifications can be obtained despite errors made by the user (FloraBase – https://florabase.dpaw.wa.gov.au/keys; Dallwitz et al. 2013). The software also includes the possibility to print a single-access key for field identification if needed, and to weight characters according to the user skills and abilities (students, general public, naturalists…). Despite the advantages provided by multi-access interactive keys, none has been produced for ladybirds so far.

This study aims to i) release the first multi-access digital interactive identification key for French ladybirds based on colour that takes into account intraspecific variability; and ii) study and discuss the discriminating power of the characters: can we identify species by colour pattern only? What are the most discriminating characters?

The work presented in this study led to the release of the first multi-access interactive digital identification key for French ladybirds. The adaptability and great number of possibilities provided by this new generation tool are unparalleled for this group, and make the key very flexible and abundantly illustrated and described, thanks to images and texts. Since it is available online and open to experts for modification, the identification key can easily be improved. It will be possible to add ladybird taxa and to extend the geographic area (e.g., a key to all European ladybirds).

Most classical and single-access keys share characters that are quite difficult to observe for students, naturalists and the general public (e.g. for ladybirds in Dauguet 1949 or Roy et al. 2013: mandibles, tooth on tibia, tarsal claws, mesosternal epimera, abdominal post-coxal lines). Here, all taxa are distinguishable with only 11 characters focusing on markings (number and shape). All characters used in this new key are visible to the naked eye or with a x10 hand lens; therefore this tool is designed for non-specialists. Using this key, most species can be identified through pictures only, as it is already the case in the identification key for the photographic survey of flower visitors (Spipoll citizen science program, www.spipoll.org), also built with Xper³.

Identification in the field is traditionally realised with paper-printed keys, but recent developments of mobile devices make it possible to use portable version of digital keys. In this perspective, the project “KeyToNature” (www.keytonature.eu) aims to develop new, more convenient and paper-free identification tools, for use within schools and universities across Europe and available on a variety of mobile platforms (laptops, smartphones). However these keys are single access, e.g., MobileKey (Weber and Hagedorn 2010) or the iRecord Ladybirds mobile application, and do not support all the possibilities provided by the free-access keys. Recently, a set of software and applications for transferring the information present in a local Xper database to an Android application has been developed (Troudet 2012). For example, the Malaco-fr application provides an interactive way to identify French snails in the field and without internet connection (Gargominy and Ripken 2011). The free-access key of French ladybirds described in this study will soon be transferred to such a mobile application, which will make it possible to use this tool in educative programs such as “Vigie-nature école” (https://www.vigienature-ecole.fr).

Both experienced and inexperienced users are likely to succeed in identifying problematic species (Morse et al. 1996, Drinkwater 2009) if they use convenient, multi-access interactive digital keys. The general public can discriminate species and several colour forms only with colour/form characters and a ×10 lens. Moreover, Xper³ provides possibilities for collaborative work and editing through its website. All the online features make it possible to update the knowledge base easily (e.g. adding numerous colour forms or acclimated species, or new characters such as ecological data). This kind of key aims to increase the curiosity of the general public, and to collect more data on the biology and distribution of species.

We thank Clémentine Dantard for the illustrations, and Frédéric Chevaillot, Fabrice Duvivier, Jean-François Godeau, David Gonzales, Donald Hobern, Guillaume Jacquemin, Julien Aït El Mekki, Andgelo Mombert, and Gilles San Martin for providing field pictures of the species. We also thank Sylvain Bouquin for his technical help with the Xper system, and Estelle Bourdon and Donald Davesne for proofreading.