Molecular characterization of interspecific competition of Diachasmimorpha longicaudata (Ashmead) and Fopius arisanus (Sonan) parasitizing the oriental fruit fly, Bactrocera dorsalis (Hendel)

Diachasmimorpha longicaudata (Ashmead) and Fopius arisanus (Sonan), are two of the most abundant and widely used parasitoids for biological control of Bactrocera dorsalis (Hendel) worldwide. However, interspecific competition between them frequently occurs within a single host once they coexit in same orchard, resulting in reduction of their combined impact. However, thus far, it is difficult to characterize these complex interactions. This paper demonstrates qPCR-methods for detection of parasitism for single D. longicaudata, and methods to determine interspecific interaction with F. arisanus. Utilizing qPCR-based methodologies, a species-specific probe was designed for D. longicaudata, which was coupled with a previously published probe for F. arisanus. An assay was developed that is sensitive enough to detect parasitism of solitary D. longicaudata across all developmental stages including one egg per host larva (0.01 ng/40 ng parasitoid/host DNA). The detected parasitism of D. longicaudata was higher than that of using traditional rearing-methods. For the lab-reared and wild strain of multiple species parasitization, qPCR-methods also detected higher parasitism by the above two species from one assay respectively when compared to conventional rearing-based methods. In the later experiment, the majority of D. longicaudata larvae were dying or dead within hollow-like host pupae probably due to interspecific competition. This method is a reliable and robust technique to determine parasitism by a single species or both species of parasitoid across all life stages within one host. It will be useful to evaluate parasitoid combined suppression, and to characterize complex interspecific competition between these two species of parasitoids.