The jewel wasp’s (Nasonia spp.) mandibular gland plays an important role in the insect’s mating behavior, as it increases female receptivity via an aphrodisiacal pheromone. Males of different Nasonia species exhibit varying behavioral patterns — differing in number of head nods and mouthpart extrusions — in delivering the pheromone to the female antennae. The fine structure of the mandibular gland and possible phenotypic trait differences linked to behavior have never been described. We expect males to have larger mandibular glands than females and presume that gland size differs between species based on behavioral patterns. This study describes the ultrastructure of the mandibular gland in Nasonia vitripennis using SBF-SEM and explores size variation in three Nasonia species (N. vitripennis, N. giraulti and N. longicornis) using 3D data from synchrotron based micro CT. The gland is atrophied in females while size varies between species for males, with N. giraulti having the largest gland, followed by N. longicornis, then N. vitripennis. Our data suggest that a larger amount of pheromone is delivered with greater frequency of head nodding and mouthpart extrusion. The male mandibular gland in Nasonia species provide a new model system for analyzing quantitative trait loci and elucidate the evolution of insect exocrine glands. Overall, this study informs the relationship between morphology and courting behavior in insects and may be applied to other pheromone producing species.