D. Walsh, a distinguished entomologist of the United States, has described what he calls phytophagic varieties and phytophagic species.    From Wordnik.com.  [II. Variation under Nature. Doubtful Species] Reference

But no observer can determine for another, even if he can do so for himself, which of these phytophagic forms ought to be called species and which varieties.    From Wordnik.com.  [II. Variation under Nature. Doubtful Species] Reference