Plants have evolved many defense mechanisms against insect herbivory in the 350 million years in which they have co-evolved.
For example, the study of herbivory on radish (Raphanus sativus) by the cabbage looper caterpillar (Trichoplusia ni) demonstrated that the variation of defensive chemicals (glucosinolates) in R. sativus, due to induction, resulted in a significant decrease in the pupation rates of T.
[5] Second, synthesizing a continually high level of defensive chemicals renders a cost to the plant.
[7] For example, the production of nicotine in cultivated tobacco (Nicotiana tabacum) has a function in plant defence.
N. tabacum plants with a higher constitutive level of nicotine are less susceptible to insect herbivory.
[14] Allocation cost is related to the channelling of a large quantity fitness-limited resources to form resistance traits in plants.
[21] Due to the consequences of induced defences on fruit characteristics, L. esculentum are less able to attract seed dispersers and this ultimately results in a reduced fitness.
Plants therefore use a variety of cues, including the sense of touch,[22] and salivary enzymes of the attacking herbivore.
For example, in a study to test whether plants can distinguish mechanical damage from insect herbivory attack, Korth and Dixon (1997) discovered that the accumulation of induce defence transcription products occurred more rapidly in potato (Solanum tuberosum L.) leaves chewed on by caterpillars than in leaves damaged mechanically.
[24] Systemically induced defences are at least in some cases the result of changes in the transcription rates of genes in a plant.
The genes encoding newly synthesised proteins after a herbivory attack can be categorised based on the function of their transcriptional products.