Reproductive Biology of Two Coelioxys Cleptoparasites in Relation to Their Megachile Hosts (Hymenoptera: Megachilidae)

We report the results of an 8-yr trap nesting study on the reproductive behavior of twocleptoparasitebees,Coelioxys funerariaSmith andCoelioxysmoestaCresson.This studyprovided a unique opportunity to examine parasite-host adaptation within a species, in which two different size classes ofC. funerariaconsistently laid eggs in thenests of the twodifferent sizedMegachilehosts, M. relativa Cresson and M. inermis Provancher. Additionally, we compared the behavior of C. funeraria to another Coelioxys, C. moesta, which also parasitized the nests of M. relativa. One striking pattern we found was the tight concordance of emergence times between hosts and parasites. The emergence patterns of individual C. funeraria parasitizing M. relativa nests closely matched that of the host, aswell as that ofC.moesta,whichparasitizes the samehost. These emergencepatternswere signiÞcantly different from those of C. funeraria on M. inermis. We also found that Coelioxys and Megachile apportioned male and female offspring in the same parts of the linear nests and at similar times of the season. Female offspring tended to be placed in the innermost cells early in the season andmales in outer cells later in the season. Because emergence patterns can severely affect offspring survival in these linear nesting situations, we suggest that the emergence times of males and females have determined the patterns of sex placement in both host and parasites.