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Global distribution of the date stone beetle, Coccotrypes dactyliperda (Coleoptera: Curculionidae, Scolytinae)

. The paper presents a compilation of the documented occurrence of the date stone beetle Coccotrypes dactyliperda across the globe. The data presented here have been compiled based on an exhaustive search of academic journal databases, collections presented in research portals and digitised holdings of national libraries. A visualisation of the global distribution shows that the presence of Coccotrypes dactyliperda is circumscribed by climatic factors.


Introduction
The date stone beetle, Coccotrypes dactyliperda (Fabricius, 1801) is a is a cryptic spermatophagus beetle of the Curculionidae family (Coleoptera: Curculionidae: Scolytinae: Dryocoetini), which was originally endemic to the Middle East where it was associated with the date palm horticultural complex After emergence from hibernation, the first generation of female beetles to leave the brood chamber emerges during late July/early August and attacks green drupes of the date palm (Phoenix dactylifera), causing the bulk of these to abscise one to two days later. The species also predates the seeds of fallen dates, often after the pericarp has been consumed by other animals, such as rodents. This continues until August, when a second generation emerges from the seeds. The rate of abscission varies, but when the infructescences are not protected from beetle attack by chemical or physical (bags) means, production losses usually range between 20 and 40%. Coccotrypes dactyliperda feeds the albumen in the seeds of a wide range of palm species. It has been documented to feed on other seeds as well but oviposition does not occur (for a review of the biology and ecology of the species see Spennemann, 2019a).
Following an unexpected mass emergence of Coccotrypes dactyliperda in a germination experiment of animal dispersed Phoenix canariensis seeds (Spennemann et al., 2018), it was necessary to carry out background research on the biology and ecology of that beetle species (Spennemann, 2019a). In the process it became clear that the species had attained a global distribution with humans as vectors. Dispersal occurred primarily in the form of date fruits for consumption, as seeds for horticultural endeavours and as vegetable ivory for button manufacture. While numerous sources made reference to the 'cosmopolitan' nature of the species, a systematic documentation of its distribution was conspicuously absent.

Material and methods
This brief study collates and places on record the documented occurrence of Coccotrypes dactyliperda across the globe. The data compiled here are based on a systematic search of academic journal databases, such as Primo, Scopus, GoogleScholar, systematic searches of Google as well as full-text searches of research portals, such as the Biodiversity Heritage Library (2018) and digitised holdings of national libraries, such as Gallica maintained by the Bibliotheque national de France (2018), or Trove maintained by the National Library of Australia (2018). Search terms were both formal (i.e. "dactyliperda + country") and informal ("common name + country"), whereby care was exercised to use both current and past country names (e.g. Sri Lanka and Ceylon, Myanmar and Burma, etc.).
In the literature the beetle is often addressed under its common names, i.e. 'date stone beetle,' 'date stone weevil,' 'palm seed borer,' 'Dattelkernborkenkäfer,' 'charançon des noyaux de dates,' 'scolyte des dates,' 'tomique du dattier' and 'palmzaadkever.' In addition, given its proclivity to also infest palm seeds that were sources of vegetable ivory used for button manufacture, the species is also known as '(ivory) button beetle' and 'Steinnusskäfer'.
As it is not possible in a compilation such as this to re-verify each original identification, and thus relies on the accuracy of the original source, it must be noted that the species identification of the instances compiled in Table 1 must be read cum grano salis.

Terminology
The status of the species in the various countries (Table 1) has been classified as follows. 'naturalised' are observations where the Coccotrypes dactyliperda have established breeding populations outside their endemic range and in the natural environment. Classified as 'introduced' are observations where Coccotrypes dactyliperda have been recorded as arriving in a given country, but where the beetles cannot establish breeding populations outside environmentally controlled environments (such laboratories, greenhouses of nurseries and store/ware houses).

Results
The systematic literature review yielded 238 references that refer to the presence of Coccotrypes dactyliperda. The compilation comprises of 214 locational entries (Table 1) in 104 countries ( Table 2). The beetle can be found on all continents bar Antarctica.

Discussion
When considering the publications chronologically, the identification and descriptive effort showed a steady increase on a decadal basis, with the effort significantly expanding in the past two decades (Figure 1). The descriptive effort changed its geographic focus over time, concurrent with increased opportunity to work outside Europe. In the nineteenth century the overwhelming majority were reports derived from European locations ( Table 2). During the twentieth century the effort expanded globally.
When considering the data geographically, we note a high number of records the areas where the beetle is endemic with every country represented, followed by a high representation in Europe (both naturalised and introduced) and Central and Southern Africa (naturalised). Other regions are less well represented (Table 3).
The documented records of the global distribution (Table 1) have been mapped in Figure 2. Plotted is the representation by country, and where available, at a state or provincial level. This visualisation shows that the presence of Coccotrypes dactyliperda is circumscribed by climatic factors. The contiguous nature of the area where it has been documented archaeologically (e.g. Costantini & Audisio, 2000;Panagiotakopulu et al., 2010) and where it can be regarded as endemic is evident. There are also clear zones both to the north and south where the species has become naturalised, as well as peripheral zones where it is on record as introduced by where it does not thrive (Table 1). These zones are circumscribed by both temperatures, in particular frost, and by humidity. A number of peripheral areas, in particular in Africa south of the Sahara (i.e. Mauretania, Mali, Niger and Chad) currently lack positive records of the beetle's presence. While given the comparative dryness in most areas this may reflect reality, it is more likely due to a lack of comprehensive research.

Acknowledgments
I am indebted to Deanna Duffy (Spatial Area Network, Charles Sturt University) for the distribution map that provides foundation for Figure 2.

Conflict of Interests
The author declares that there is no conflict of interest regarding the publication of this paper.