Insect identification, Chennai, India
To me, it looks like a Lepidoptera from the Sphingidae family (Hawk moths). It is similar to species in Hemaris and might belong to this genus.

One similar species from this genus (found in India) is Hemaris tityus, but the moth in your picture doesn't look exactly like this particular species. Another similar species is Hemaris saundersii, which is found in and around India.



(Hemaris tityus, pic from wikipedia)