Copidosoma floridanum (Hymenoptera: Encyrtidae) represents a developmental extreme among the polyembryonic wasps of Hymenoptera. Within Encyrtidae, a single egg proliferates to several thousand adult wasps while forming two distinct larval castes: reproductive and precocious. However, the regulatory systems that control proliferation remain unknown. To explore potential mechanisms, we employed the candidate gene approach, focusing on the Hedgehog (Hh) signal transduction pathway as a prime candidate. Among metazoan taxa, one function of Hh is to regulate cellular proliferation during development. For example, within Drosophila, Hh has been shown to control the proliferation and differentiation of somatic stem cells within the ovary. Hh has also been implicated in proliferation throughout vertebrate development and in the formation of many cancers.  Using PCR, a 149 bp fragment of C. floridanum hh (Cf-hh) was cloned with degenerate primers. Temporal expression patterns were characterized using RT-PCR. Cf-hh mRNA was expressed throughout polyembryonic proliferation of C. floridanum, as well as during embryonic segmentation of the reproductive embryos.  In situ hybridization characterized spatial expression patterns using DIG-11-UTP labeled riboprobes.  Cf-hh mRNA was detected in proliferating morulae from the first through third host instar, while expression was absent in differentiating, precocious morulae.  Expression of Cf-hh mRNA was not detectable when proliferation ceased at the onset of the fourth host instar.  Data from both RT-PCR and in situ hybridization strongly suggests Cf-hh has a role in cellular proliferation during polyembryonic development of C. floridanum.