Host plant

What is a host plant?

One question frequently asked is why are some plants attacked by a herbivore and other plants left untouched. Within this simplequestion are two linked questions,

The Plant-SyNZ™ database is concerned with documenting the host plants of herbivores and this information may give clues as to why some plant species are hosts and others are not.

For the Plant-SyNZ™ database, a host plant is a plant species on which at least one life stage of a herbivore feeds without being harmed and can pass on to the next life stage or lay fertile eggs. For an explanation of the criteria used to decide if a plant is a host for a herbivore, go to the page explaining the use of a reliability index for the quality of this information. A more detailed discussion about criteria used for deciding if a plant species is a host of a herbivore can be found in the following paper: Ward LK. 1988. The validity and interpretation of insect food plant records. British Journal of Entomology and Natural History 1 (4): 153-162.

The database only shows whether a plant can be a host for a herbivore, it does not provide information on the relative abundance of a herbivore on different host plant species. All host plants listed for a herbivore are not equally good hosts, e.g. leaf mines of Chromatomyia syngenesiae (Diptera: Agromyzidae) are commonly seen on Sonchus species, Senecio bipinnatisectus and S. jacobaea (ragwort), but, are rarely seen on Senecio vulgar (groundsel) or S. skirrhodon.

Why are some plants of a host plant species infested and others are not?

Herbivore numbers can change during the year because of the breeding cycle of the herbivore, but infestation rates can also vary between plants at a similar stage of the herbivore's annual cycle.

There are four main reasons for variable infestation of plants by herbivores, plant resistance, environment, natural enemies and chance. On a local scale, without careful experimentation it can be very difficult to determine the relative importance of eachof these factors.

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