The phrase "staggering capacity to reproduce" implies an impressive or extraordinary ability to multiply. The word "overwhelming" captures the idea of being very great or intense, suggesting a significant and powerful capability to reproduce in large numbers.

Therefore, option D, "overwhelming multiplying power," is the most suitable choice as it aligns with the notion of an extraordinary and powerful capacity for reproduction.  Staggering in this context does not function as verb. Staggering here functions as an adjective which means 'incredible, overwhelming, or amazing' Options A, B, and C do not convey the same sense of impressive and intense multiplying power as the word "overwhelming" does.