Abstract: Insects and plants are important components of the terrestrial biocommunities on the globe; living together they perform diversified interactions including patterns of insectan trophic activity and mode of pollination. In this paper the relationship between these interactions and evolution is discussed. According to the breadth of hostplant range, phytophagous insects are usually classified into specialists (with narrow host range) and generalists (with broad host range). If the seemingly advantage to feed on many different plants by insects is considered, the generalists would be regarded to attain a higher level of evolution. However, a careful examination on the biocommunities in nature usually gives rise to the hard question of why there are so many specialists among insect herbivores. The explanation seems to lie in the higher efficiency of hostplant foraging and the ease of escaping or avoidance from natural enemies in the specialists. Plant adaptation to insect herbivory presumably would cause corresponding reactions in insects, leading to the proposals of coevolution theory. For hostplant selection by insects, several theories are proposed to clarify the present status as paired reciprocal, diffused and community coevolutions. The precedence of diversification of secondary metabolic chemicals in plants and the mutability and adaptation in insect sensory function as well as learning and memory also lead to the proposal of the theory of sequential evolution or colonization. In pollination the mutualistic adaptations between flowers and pollinator insects are manifested in convincing examples including the changing signalling cues from flowers as scents, colors in different plant species, and the blooming schedules, and the behavioral responses and structural modifications of the pollinator insects.

Key words: insect-plant relationship, hostplant selection, pollination, coevolution