Q. I work on science textbooks and science trade books (I wonder why I’ve never needed to ask this question before) and have this question: Does one capitalize “sp.” (or “spp.”) in titles? For example: “Dinarda Spp.: The Sneaky Thief.” Unabbreviated, the word “species” would be capitalized. However, were it the actual species name, it would be lowercased. It does look odd capitalized, since it is never so in text, but I’m leaning toward capitalization as being correct. Possibly the answer to this question lies within (within CMOS, that is), but if so I’ve not been able to find it. What say you?
A. As of the 18th edition, we cover this situation in CMOS 8.160, rule 7:
Lowercase the second part of a species name, such as fulvescens in Acipenser fulvescens, even if it is the last word in a title or subtitle (and including the abbreviations “sp.” and “spp.” used in place of the second part of the name; see 8.124).