Solution

Insects are classified into mainly three categories on the basis of the orientation of the head in its resting position, with respect to the long axis of the insect body. These are -

Prognathous: These insects have their head horizontally oriented and the mouth-parts are pointed anteriorly.
Example - Carabid Beetles, Earwigs, etc.

Hypognathous: These insects have their head vertically oriented and the mouth-parts are pointed ventrally downwards.
Example - Cockroach, Grasshopper, Housefly, Honey Bee, etc.

Opisthognathous: These insects have their head obliquely oriented and the mouth-parts pointed ventroposteriorly rearwards.
Example - Leafhoppers, Aphids, Whiteflies, etc.