Reproductive biology of two Coelioxys cleptoparasites in relation to theirMegachile hosts (Hymenoptera : Megachilidae)

We report the results of an 8-yr trap nesting study on the reproductive beh avior of two cleptoparasite bees, Coelioxys funeraria Smith and Coelioxys m oesta Cresson. This study provided a unique opportunity to examine parasite -host adaptation within a species, in which two different size classes of C . funeraria consistently laid. eggs in the nests of the two different sized Megachile hosts, M. relativa Cresson and M. inermis Provancher. Additional ly, we compared the behavior of C. funeraria to another Coelioxys, C. moest a, which also parasitized the nests of M. relativa. One striking pattern we found was the tight concordance of emergence times between hosts and paras ites. The emergence patterns of individual C. funeraria, parasitizing M. re lativa nests closely matched that of the host, as well as that of C. moesta , which parasitizes the same host. These emergence Dat tel ns were signific antly different from those of C, funeraria on M. inermis. We also found tha t Coelioxys and Megachile apportioned male and female offspring in the same parts of the linear nests and at similar times of the season. Female offsp ring tended to Le placed in the innermost cells early in the season and mal es in outer cells later in the season. Because emergence patterns can sever ely affect offspring survival in these linear nesting situations, we sugges t that the emergence times of males and females have determined the pattern s of sex placement in both host and parasites.