Reliability score

What is the reliability score?

The information to support a particular invertebrate herbivoresassociation with a particular plant varies in quality and therefore reliability.

In the best case there is excellent evidence that the herbivore successfully breeds on the plant. In the worst case an adult has been found sitting on a plant leaf with no evidence of feeding, rather like finding a beetle resting on washing hanging on the line. The presence of the beetle on washing is not evidence for feeding or breeding.

In the Plant-SyNZ database a reliability score of 0 to 10 is used, with 10 being high quality evidence supporting a herbivore-host plant association. 0 is used for published associations that are subsequently shown to be wrong. The database also gives the reason/evidence for the score, who gave the score and the date when it was given. The score is subjective and is based on expert interpretation of each relationship (see below for details). Care needs to be used when interpreting the reliability score.

The Plant-SyNZ database does not provide information on the relative suitability of host plant species for a herbivore. See "What is a host plant?" for a discussion of host plants.

How to use the reliability score

When generating a report from the database, you can select for the quality of host associations that you require. You can choose to have all the host associations for a selected plant or herbivore species, or you can choose to have only host associations with a minimum score i.e. 5 and above or 7 and above.

Reports with and without reasons for the scores

All the reports from the database will show the reliability score. However, you can choose whether or not to have the reasons for the score. This option "without reasons" allows for more compact reports, the option "with reasons" allows the user to understand why a score was given and to better decide how to filter the lists using the reliability score.

What criteria are used for reliability scores?

The criteria that can be used for reliability scores varies according to the biology of each group of herbivores. For example, juvenile whitefly stay on the leaf on which the egg is laid, and are identified from the puparium. The presence of whitefly puparia on a plant is excellent evidence that the plant species is a host and the association is given a score of 10. If the plant can only be identified to genus, the score is reduced to 7. Similarly other scale insects that stay on the same plant for all their life stages would score 10 if the adult female is found on a plant species.

Insects and mites with more mobile adult and juvenile stages need more judicious consideration.

Mites, especially those associated with galls need careful observation and good evidence of breeding on the plant to be certain of a host association. Where a gall is involved, the best evidence is from breeding mites found in the newly formed gall. Once a gall has matured, it may be invaded by other invertebrates, including other gall mites that then use it as a shelter, but do not necessarily breed on the plant.

Caterpillars ideally should be found on the suspected host plant and reared on it to maturity and the moth identified. Care needs to be taken when large, almost mature caterpillars are found on a plant; the plant may not be a primary host. Some large caterpillars can feed on plants that do not support the growth of all stages of the species.

Leaf feeding beetles. Some beetles such as Chrysomelidae and some weevils have adults that feed on leaves, but the larvae have different or unknown habits. Adults may be found on a plant with typical feeding damage for that kind of beetle. However, it is advisable to check that the beetle does feed on the plant by putting the adult beetles in a container such as a plastic bag or lidded jar with undamaged leaves. If after a day the leaves exhibit feeding damage of the kind seen on the host plant, then this can be regarded as good evidence for a host association and not a chance occurrence on the plant.

Gall forming insects and leaf miners need to be reared to identify the insect and hence the host association. In some cases a distinctive gall or mine may be found on another plant species in the same genus and a tentative host association created with a score of 5 or 6 depending upon the circumstances.

Aphids. The presence of wingless females or winged forms with colonies can provide good evidence for a host association.

Thrips and mobile sucking bugs. The presence of adults and juvenile stages of the same species is good evidence of a host association, though it is possible the species may be partially or wholly predacious. It is important that, where possible, the juveniles are reared to maturity on part of the plant. Juveniles in the absence of adults should, of course, be reared to maturity.


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