Table 1.

Functional categories of plant-herbivore interaction.^a

Functional category	Definition	Effects on herbivoresb	Effects on plantb	Estimated in this study
Susceptibility	Inability of a plant to deter or defend against damage from herbivores	No negative effects	Normally high damage	Comparison of damage (biomass loss) against resistant variety
Resistance	A plant trait that reduces potential damage from herbivores compared to susceptible plants	Relative decline in fitness through antixenotic or antibiotic effectsc	Relative decline in damage	Comparison of damage (biomass loss) against susceptible variety
Antixenosis	Plant traits (mechanisms) that deter herbivores from ovipositing or from initiating feeding	Relatively low oviposition and/or feeding preferences	Relative decline in damage	Not estimated here (requires choice bioassays)
Antibiosis	Plant traits (mechanisms) that adversely affect the survival, growth or reproductive output of herbivores	Relative decline in survival, biomass, development time, or fecundity	Relative decline in damage	Comparisons of oviposition, nymph survival, nymph biomass, development times, and feeding efficiency (honeydew) with susceptible variety
Tolerance	A plant's capacity to withstand herbivore damage and continue to grow and/or yield satisfactorily during and after herbivore attack	No negative effects	Maintains relatively high growth rates (biomass) or reproductive output (yield) per unit of herbivore biomassd	Estimated as the relative decline in plant fitness per unit weight of planthopper across a gradient of environments

^aFor further details see Strauss and Agrawal (1999) and Smith (2005).

^bComparative effects relative to a susceptible variety.

^cFitness is a quantitative representation of reproductive success (genetic contribution to future generations through survival and development × reproductive output) in a given environment.

^dObserved during low levels of intraspecific competition between herbivores.