How to interpret foodplant records

Lists of foodplant records for a herbivore, or of invertebrates on a host, must be interpreted carefully in the context of your study. The guidance below aims to help you make sense of search results.

An in-depth discussion on the interpretation of records in the original PDIB database can be found in Lena Ward’s 1988 article, ‘The validity and interpretation of insect foodplant records. British Journal of Entomology and Natural History, Vol. 1, pp. 153 – 162’.

Validity of records

There are three categories for the validity of interactions in DBIF:

• ‘Good’ interactions, which are included in the outputs of database searches.

• ‘Unreliable’ interactions, which are excluded from outputs. Where doubt about an interaction has been expressed by the original, or later, authors.

• ‘Deleted’ interactions, which are excluded from outputs. Where authors have stated that an interaction is incorrect. During the 2007-08 update of certain families in DBIF, records with old nomenclature were also labelled ‘deleted’, and then duplicated with the new names. This allows the names, as given in the original source, to be traced.

Unreliable and deleted interactions can be included in search outputs if they are requested.

Attributes associated with interactions

The extensive information associated with interactions is essential for interpreting the host plant records. See Ancillary information: attribute data for comprehensive lists related to interactions, and invertebrate and host names. Each interaction is at least labelled with its geographical location, and with the invertebrate’s life-cycle stage and trophic level.

Some of the more important attributes to think about when generating / interpreting lists of interactions are covered below [sub-headings could be links to text, so that user can scan list quickly instead of scrolling through text]:

Geographical location of interactions

The database contains interactions recorded in Great Britain, continental Europe, North America and elsewhere in the world. If no location information was provided in a source, then the record was labelled ‘no location’ (see family backgrounds for the proportions of species and interactions which have British data).

Foreign records were generally used to fill gaps in the British data. However, if foreign data are used in outputs, the range of hostplants for a species is likely to be wider than has been recorded in Great Britain alone. This is because Great Britain only holds a subset of the European flora, so numerous related hosts are missing, or because the greater area of continental Europe allows more regional variation in host choice (Also, many herbivores at the edges of their ranges in Great Britain will occupy a wider range of habitats on the continent).

Variation in host choice also occurs within species in Great Britain. It is most evident at the level of sub-species and forms (visible in the well-recorded butterflies).

Captive breeding records

Herbivores will tend to feed on a wider range of hosts in captivity than has been recorded in the wild, i.e. host lists for species, or species lists for hosts, which include captive breeding records will be artificially inflated. This should be considered in the context of a study before captive breeding records are included.

Non-herbivorous species in DBIF

While DBIF is primarily a compilation of the host plants that invertebrates need for completing their development (i.e. from immature stages to adult), numerous closely associated species, which do not feed directly on a plant, are included in the database. Such species may depend on a herbivore as predators, parasitoids, mutualists or inquilines.

All of the interactions in DBIF are labelled with the trophic level of the invertebrate. The trophic level may vary within a species, depending on the interaction, e.g. if the invertebrate is an omnivore.

Life-cycle stages

While DBIF mainly concerns the immature stages of herbivores, it also includes interactions for various grades of adults:

• Adults feeding on the same host as the immature stages (as in hoppers, aphids and scales)

• Adults feeding on a wider range of related hosts (as in many beetles)

• Adults feeding on different resources altogether, such as nectar or pollen (as in many butterflies and moths, hoverflies, or thrips). Interactions for adults feeding at nectar, pollen, fruit or sap do occur in DBIF. It is sometimes possible for secondary literature sources to present these interactions as hosts for the entire life-cycle.

Some knowledge of the invertebrates you are dealing with may therefore be useful in interpreting adult relationships, and their specificity to a host plant (see Invertebrate families for some background). For example, several plant-lice families (Psylloidea) overwinter as nymphs or adults on ‘shelter’ plants, which are not used as hosts for development.

Alternating generations

invertebrates have distinct generations that use hosts in different ways, such as host-alternating aphids and oak-gall wasps. In DBIF, these generations are treated as separate taxa:

• for aphids (Aphidoidea), the species name is followed by ‘I’ or ‘II’ to represent generations on primary or secondary hosts.

• in oak-gall wasps (Cynipidae), the agamic generation is labelled as such.