Synopsis Functional dynamics of insects relate to diverse aspects of host plant selection behaviour emphasizing the role of sensory physiology, biochemical attributes and energetics in the regulation of feeding and reproduction. The ability of phytophagous insects to perceive numerous chemical compounds in plants through a highly developed chemosensory system appreciably influences the choice of the food plant. Versatility is an essential prerequisite in insects to complete all the normal sequence of events in the host selection process, involving colonization, fecundity, growth and population build-up. All the same, plants co-evolving with their insect pests tend to acquire a certain degree of resistance to enable their survival. Insects being endowed with the capacity to adapt themselves and respond to finely tuned and broadly tuned systems, selection of potential hosts is decided by a balance between the physiological and chemical stimuli, so that recognition and preference of host plants involve integration of complex neural and metabolic events. Diverse facets of functional dynamics from phytochemicals as messengers altering behaviour through energetics and resource allocation to mutualistic interactions between host plants and third trophic levels are discussed.