Lokesh is an expert in the studies of reptiles and amphibians. Lokesh is a/an:

Dermatologist ==> a doctor who studies and treats skin diseases.

Entomologist ==> a person who studies or is an expert in the branch of zoology concerned with insects.

Ornithologist ==> a person who studies or is an expert in the branch of zoology concerned with birds.

Herpetologist ==> a person who studies or is an expert in the branch of zoology concerned with reptiles and amphibians.

As per the above definition of the given words, we can say that Lokesh is a Herpetologist.