Abstract
Growth, reproduction, and survival are fundamental biological priorities that animals balance by evaluating dietary cues. Cholesterol occupies a unique position among nutrients, serving both as a structural component of cellular membranes and as a precursor for steroid hormones, yet its regulation differs fundamentally across taxa. In mammals, cholesterol availability is buffered by endogenous synthesis and post-ingestive metabolic control. In contrast, insects have evolutionarily lost sterol biosynthesis and are therefore sterol auxotrophs that rely entirely on dietary sources. Here, we synthesize current understanding of cholesterol biology in Drosophila melanogaster, with a focus on sterol auxotrophy, life-stage-specific allocation, and endocrine and lifespan outcomes in a comparative framework. We highlight cholesterol not only as a metabolic substrate but also as a sensory-encoded nutrient that shapes feeding behavior. We further examine how lipophorin (Lpp)-mediated transport, Niemann-Pick type C proteins, ATP-binding cassette transporters, and the nuclear receptor DHR96 coordinate systemic sterol distribution and endocrine output in the absence of endogenous synthesis. By integrating these mechanisms across development, we illustrate how cholesterol availability governs larval growth, ecdysteroid production, adult reproduction, neural function, and lifespan through coupled endocrine and nutrient-signaling networks. This review positions cholesterol as a multifunctional signal linking sensory perception, metabolic regulation, and life-history strategy in sterol-auxotrophic insects, offering a framework for understanding how evolutionary loss of biosynthetic capacity reshapes nutrient sensing and homeostatic control.
