Toxoptera citricida or Toxoptera citricidus?
A recent paper from Nieto Nafría et al. (2005) provides useful explanations and arguments about the correct nomenclature which should be used for the brown citrus aphid. In 1907, the species was first described from Hawaii (US) on Citrus by Kirkaldy as Myzus citricidus (the name was chosen to mean citrus-killer). In 1938, Takahashi reassigned it to the genus Toxoptera. In 1994, Stoetzel considered that the correct name should be Toxoptera citricida because in Latin ‘citrus-killer’ (citricida) should be constructed in a similar way as ‘fratricida’ or ‘suicida’, etc. which are nouns deriving from verbs, and therefore which do not change for gender accord. Moreover, the name ‘citricidus’ was originally proposed as a latinized adjective with a masculine ending to match the genus name (Myzus is masculine in Latin whereas Toxoptera is feminine).
But in the current International Code for Nomenclature, it is said that if the author has not indicated whether the name was regarded as a noun or an adjective (which is apparently the case for M. citricidus), the name should be treated as a noun in apposition to the name of its genus (the original spelling is to be retained, with gender ending unchanged), and that incorrect latinizations are not to be considered inadvertent errors (such errors would otherwise need to be corrected). In addition, the prevailing use is more in favour of T. citricidus (e.g. 55-60% of the records of the species on the web are T. citricidus). Therefore, the original spelling ‘citricidus’, although an incorrect latinization, should be retained. In conclusion, Nieto Nafría et al. considered that the correct spelling of the species name is Toxoptera citricidus (Kirkaldy) and that T. citricida should be considered as a synonym.
Sources
Nieto Nafría JM, Alonso-Zarazaga MA, Pérez Hidalgo N (2005) Nomenclatural Notes. Toxoptera citricida or Toxoptera citricidus? The validity of a specific name (Hemiptera, Aphididae, Aphidini). Graellsia 61(1), 141-142.