Odorant-binding protein gene activity in the larval castes of the polyembryonic wasp Copidosoma floridanum

The polyembryonic wasp Copidosoma floridanum produces soldier and reproductive larval castes during development within its caterpillar host. Caste-bias in the expression patterns of 8 Copidosoma odorant-binding protein (OBP) genes was examined using reverse transcription-polymerase chain reaction (RT-PCR) and in situ expression studies. Six of the 8 genes are clearly biased in their expression towards one or the other larval caste. Three distinct in situ probe hybridization patterns were observed in this study.  None of the tissues showing clear expression of OBP genes are known to have a chemosensory function. Two of the expression patterns suggest the majority of the OBP genes come into contact with host hemolymph. Further, one of these expression patterns was uniquely associated with the extra-embryonic membrane encompassing each of the reproductive larvae. The absence of expression in the membrane surrounding soldier larvae suggests the majority of the OBPs characterized in this study are performing caste-specific functions within the host.