The food plant dataset

This dataset (Suppl. material 1) is a synthesis of current knowledge regarding the food plants eaten by the caterpillars of two families of Lepidoptera (Saturniidae and Sphingidae). It aims to capture the state of knowledge at the time of assembly of the dataset so that it can be used to investigate the role of food plants use breadth in the spatial and temporal evolution of both families (Arnal et al., in prep.).

This dataset of larval food plant records for sphingids and saturniids worldwide is the result of the integration, with significant data reconciliation and standardisation, of these three largely independent data sources:

1) Information for Sphingidae and Saturniidae embedded in the HOSTS database (Robinson et al. 2010); as further added to and refined by IJK, downloaded on 2 March 2018) (hereafter HOSTS);

2) An inventory of the caterpillars, their food plants and parasitoids of Area de Conservacion Guanacaste (ACG, Janzen DH, downloaded on 16 July 2018 for Saturniidae and 18 July 2018 for Sphingidae) (hereafter DHJ);

3) The personal database of Jean Haxaire (Associate Researcher to MNHN, imported on 17 July 2018) (hereafter JH).

A “record” refers to a unique combination of caterpillar species, plant species and source. Records in the dataset resulting from rearing experiments in captivity or from introduced plant species are listed separately as they often do not represent natural insect-plant associations. Redundancy (duplication) of records amongst the three databases following their combination was not a concern for our research objectives; the dataset should be treated as qualitative and the frequency of records ignored (see list of points in next section).

A total of 25,937 records was compiled from the three databases in a single dataset given as Suppl. material 1. Table 1 below provides details of the number of records contributed by each of the independent databases. We followed the plant taxonomy of the International Plant Names Index (IPNI; https://www.ipni.org) and the latest moth taxonomy (Kitching et al. 2018), though both do not coincide with some of the names used by all three sources (see 'call for caution' below).

This compilation provides information for 137 genera and 757 species of Saturniidae and 166 genera and 725 species of Sphingidae.

As an example of the uses of this dataset, we report basic polyphagy variables as well as a polyphagy score, based on the Phylogenetic Diversity (PD, Faith 1992) of the food plants used by the caterpillars of saturniid and sphingid moths. Using a recent dated angiosperm phylogeny (Magallón et al. 2015), we measured the PD score, i.e. the total length of all phylogenetic tree branches connecting the different families of plants eaten by a given moth species in natura, using the pd function of the picante R package (Kembel et al. 2010). The species scores were then averaged within each genus to obtain genus scores in Suppl. material 2. Note that gymnosperm records were excluded from our calculations of PD scores to avoid bias caused by the considerable phylogenetic distance between angiosperms and gymnosperms.

The genus-level polyphagy variables and the polyphagy scores of Saturniidae and Sphingidae genera are provided as Suppl. material 2.

Calls for caution:

1. The correctness of food plant identifications in databases and in literature should be treated with considerable caution, as they were largely made by non-botanists; food plant names used are also subject to taxonomic and nomenclatural uncertainty and their correctness and validity may be considered equivocal in some cases.
2. The previous point also applies to moth names, especially when considering species-level identifications. These may be incorrect or outdated. For example, more than 1500 new species have been described within family Saturniidae in the past decade (Kitching et al. 2018), largely with the support of DNA barcoding analyses. Thus, food plant records may not account for recently split complexes of cryptic species, members of which may have quite different natural histories (e.g. Janzen (2012)).
3. The food plant dataset is derived from known food plant records at the time of its compilation; as such, it represents a snapshot of the knowledge at that time and it may differ from the data compiled in the original sources and then updated independently (e.g. new records and/or corrections (e.g. identification errors or synonymies of the moth/caterpillar or the plant or both)).
4. All records are meant to represent actual instances in which caterpillars were found feeding and developing on the food plant. Records in the DHJ database all result from rearing trials of caterpillars found in the field on the food plant in question and, in many cases, identification of the caterpillar was confirmed through DNA barcoding of the resultant adult moths. A few records, recognised as questionable (e.g. inconsistent locality/identification data) in the HOSTS and JH databases, were filtered out and are not included in the present combined dataset.
5. The food plant dataset does not account for the frequency of use of a given food plant amongst other plants also listed for the same species of moth. The DHJ database, because it is based on individual specimen records, does include quantitative data; however, this information is not incorporated into the combined dataset, although it could bring additional information on local food plant preferences of species and populations. We note that this information would nevertheless be very difficult to analyse and interpret as it is conditional upon the local availability of food plants, as well as possibly seasonal conditions, local variations through time and difficulty of collecting.
6. The previous point also brings a note of caution in that polyphagy, as calculated here from the data available for a given species, may not be translatable to the population or site level and vice versa. A species may have populations in which some caterpillars have a lower level of polyphagy than others, at least in part because the food plants that could be eaten do not occur in that ecosystem and because many species arrive by ecological fitting rather than in situ evolution (Janzen 1985a). This is especially the case with species following expanding frontier agriculture into new ecosystems or following contemporary climate changes.
7. Strictly speaking, we define polyphagy as the capacity of a given individual caterpillar to feed and develop (through its complete life cycle) on different food plants. This can only be approximated by considering sibling individuals (as is sometimes the case in the DHJ database), individuals from the same population or, ultimately, from the same species or higher taxonomic categories. We thus acknowledge that the scores of polyphagy at species and genus level should be recognised as human abstractions.
8. Polyphagy is constrained in situ by the local availability of food plants - an individual caterpillar cannot be polyphagous on species of plants that are not present.
9. Here we approximated polyphagy scores at species level for saturniid and sphingid moths and we assume that they represent valuable information about the level of plasticity of individuals of the populations of a species to use different food plants. These scores were then used to calculate polyphagy scores at the genus level. Generic level of polyphagy is a human abstraction, but it is seen as relevant information to understand the past diversification dynamics. Plasticity in the use of food plants may have favoured or impeded geographical dispersal and may have mitigated speciation or extinction processes or influenced species' natural histories in many other ways (Janzen 1985b).
10. We acknowledge that the polyphagy level derived from caterpillar plant feeding records approximates, but may not reflect precisely, the plasticity in oviposition site selection by female moths (see, for instance, Janzen 1984b). Indeed, caterpillars may be driven by starvation to feed on a different plant after consuming all leaves of the plant they started to develop on and which had been selected for oviposition by the female.