answer) Every bite an herbivore takes comes at the expense of a
plant. Some plants avoid herbivory by decreasing their apparency or
‘hiding' from herbivores in spatial or temporal refuges. Spatial
refuges are areas physically inaccessible to or hidden from
herbivores as when plants grow on cliff ledges and plateaus in the
case of geologic refuges.
First, some plants can release volatile organic chemicals (VOCs) that mask or overpower VOCs released by another plant that would normally attract herbivores. Second, plants may provide an alternate food source that draws herbivores away from another plant, an effect referred to as the alternate host hypothesis in which associational resistance for one plant species is paired with associational susceptibility in another plant species.
Once herbivores find and access a plant, structural defenses can discourage consumption. These structures include spinescence, trichomes, thick leaves, and microscopic sand- and needle-like particles inside plant tissues
Instead of directly defending against herbivores, indirect defenses reduce herbivory by increasing the likelihood that herbivores (usually insects) are attacked, removed, or harassed by predators like ants, wasps, and mites. Plants increase predation of herbivores by luring and keeping predators on a plant with food rewards, shelters from harsh conditions, or chemicals signaling prey availability.
answer) Insect resistance refers to crops that either
naturally or through genetic engineering are able to resist insect
damage. Insect-resistant crops generally produce compounds that are
toxic to insects that attempt to eat the resistant plants.
Bacillus thuringiensis is a major source of insecticidal genes imparting insect resistance in transgenic plants. Pest resistant GM crops (primarily cotton and maize), have been genetically modified so they are toxic to certain insects. They are often called Bt crops because the introduced genes were originally identified in a bacterial species called Bacillus thuringiensis.