Which insects are phytophagous in nature?

The correct answer is Option (4) → Insects which feed on plant sap and other parts of plants.

“Phyto” means plant and “phagous” means eating. Phytophagous insects feed on plant sap and other parts of living plants. Nearly 25 per cent of all insects are phytophagous. For plants, such herbivores are the predators, and this is why plants have evolved thorns and chemical defences.

Option (1) Insects that live on the animals. — Incorrect. Insects that live on animals and feed on them, such as lice, are ectoparasites of animals. They do not eat plants.

Option (2) Insects that feed on dead plant tissues. — Incorrect. Organisms that feed on dead plant remains (detritus) are detritivores, such as earthworms. Phytophagous insects feed on living plants.

Option (3) Insects which live on epiphytes. — Incorrect. Epiphytes are plants that grow on other plants, such as orchids on a mango branch. Living on an epiphyte only describes where an insect stays, not what it eats.

Option (4) Insects which feed on plant sap and other parts of plants. — Correct. Feeding on plant sap and other parts of plants is the book’s meaning of phytophagous.

NCERT Extract:
Population Interactions – “… For plants, herbivores are the predators. Nearly 25 per cent of all insects are known to be phytophagous (feeding on plant sap and other parts of plants). The problem is particularly severe for plants because, unlike animals, they cannot run away from their predators.”