Herbivore adaptations to plant defense

[2] The escape and radiation mechanisms for coevolution, presents the idea that adaptations in herbivores and their host plants, has been the driving force behind speciation.

[3][4] The coevolution that occurs between plants and herbivores that ultimately results in the speciation of both can be further explained by the Red Queen hypothesis.

[7] Within the family Sphingidae (sphinx moths), it has been observed that the caterpillars of species which eat relatively soft leaves are equipped with incisors for tearing and chewing, while the species that feed on mature leaves and grasses cut them with toothless snipping mandibles (the uppermost pair of jaws in insects, used for feeding).

This morphological difference can be explained by the fact that insoluble tannin-protein complexes can be broken down and absorbed as nutrients at alkaline pH levels.

[10] Herbivores generate enzymes that counter and reduce the effectiveness of numerous toxic secondary metabolic products produced by plants.

One such enzyme group, mixed function oxidases (MFOs), detoxify harmful plant compounds by catalyzing oxidative reactions.

One group linked herbivore feeding on plant material protected by chemical defenses with P-450 detoxification in larval tobacco hornworms.

[12] The induction of P-450 after initial nicotine ingestion allowed the larval tobacco hornworms to increase feeding on the toxic plant tissues.

The protease enzyme is a protein in the gut that helps the insect digest its main source of food: plant tissue.

Protease inactivation can lead to many issues such as reduced feeding, prolonged larval development time, and weight gain.

The enzyme glucose oxidase, a component of saliva for the caterpillar Helicoverpa zea, counteracts the production of induced defenses in tobacco.

[17] Similarly, the cotton leaf perforator selectively avoids eating the epidermis and pigment glands of their hosts, which contain defensive terpenoid aldehydes.

For example, fungal symbionts of cigarette beetles (Lasioderma serricorne) use certain plant allelochemicals as their source of carbon, in addition to producing detoxification enzymes (esterases) to get rid of other toxins.

[1] As an example, several species of bark beetle introduce blue stain fungi of the genera Ceratocystis and Ophiostoma into trees before feeding.

[23] The blue stain fungi cause lesions that reduce the trees' defensive mechanisms and allow the bark beetles to feed.

For example, caterpillars from the families Pyralidae and Ctenuchidae roll mature leaves of the neotropical shrub Psychotria horizontalis around an expanding bud that they consume.

These canal systems store fluids under pressure, and when ruptured (i.e. from herbivory) secondary metabolic products flow to the release point.

This technique minimizes the outflow of latex or resin beyond the cut and allows herbivores to freely feed above the damaged section.

[37] Additionally, secondary metabolic products can act as cues to identify a plant for feeding or oviposition (egg laying) by herbivores.