Rhagastis castanea (Moore, 1872)

Transferred to Theretra by Rothschild & Jordan, 1903, Novit. zool. 9 (suppl.): 764 (key), 788. Transferred to Rhagastis by Melichar et al., 2018, A field guide to hawkmoths of the state of Karnataka, India: 100. When transferring Theretra castanea from Theretra to Rhagastis, Melichar et al. (2018) (STI 21973) simply stated “All the characters of this moth (both larval and imaginal) indicate it is a Rhagastis”; they did not state what those characters were. When Rothschild & Jordan (1903) (STI 19807) originally described Rhagastis, they, stated that it “differs from Theretra in the second segment of the [labial] palpi not touching one another, the base of the tongue remaining visible; from Cechenena [which then included several species not placed in Cechetra] in these segments not being so narrow, bearing a large apical tuft on the innerside, and having a much smaller naked area”. However, in the species entry for Theretra castanea, Rothschild & Jordan (1903: 789) noted that “the species leads over to Rhagastis, which it resembles very much in shape and in the style of coloration” (e.g., Rhagastis olivacea). They made no explicit mention of the condition of the labial palps, which they presumably interpreted as showing the Theretra condition, in which they come together to conceal the base of the proboscis. Consequently, they transferred Pergesa castanea to Theretra, despite the species’ superficial resemblance to certain Rhagastis. Examination of the series in NHMUK has shown that Rothschild & Jordan (1903) were correct in their observation that the labial palp scaling in Rhagastis castanea closes over and hides the base of the proboscis. Thus, by transferring the species to Rhagastis, Melichar et al. (2018) have rendered that genus undiagnosable morphologically. However, the closed condition of Rhagastis castanea is found in most other Sphingidae and is likely to be the plesiomorphic condition of this character. Thus, it is not evidence to support the inclusion of Rhagastis castanea in Theretra. Rhagastis castanea may be the sister-group of all other Rhagastis, which form a monophyletic group based on the putative synapomorphic open palp condition. Further study is clearly necessary to resolve this question more satisfactorily.