A large-scale comparison of conventional and molecular methods for the evaluation of host-parasitoid associations in non-target risk-assessment studies.
Accurate identification of natural enemies is the cornerstone of biological control, and methods that can separate closely related species are essential in ecological studies of parasitoids. Conventionally, host rearing and dissection are used to define the ecological host range of candidate biological control agents and assess host-specificity of parasitoids. However, molecular methods may be more suitable for the evaluation of host-parasitoid associations. To demonstrate the utility of molecular diagnostics in ecological host-range studies on parasitoids of Lygus plant bugs, host rearing, dissection and multiplex polymerase chain reaction (PCR) analysis were used to estimate parasitism levels and parasitoid species composition (genus Peristenus) in more than 26 000 field-collected target and non-target Miridae. Parasitism levels estimated by conventional and molecular methods were similar but molecular analysis can detect parasitoids earlier than dissection and rearing. Parasitoid pupal mortality prevented the identification of more than 30% of individuals reared from non-target host material; however, paired samples analysed with the multiplex assay allowed the identity of these parasitoids to be inferred. Molecular methods can provide different, and generally more complete, parasitoid species composition information because the results are not confounded by the host and parasitoid mortality encountered in rearing. However, detection of a parasitoid in a host does not necessarily indicate survival to the adult stage. Further, molecular identification of parasitoid species may be restricted to those species for which PCR primers are available. Synthesis and applications. For molecular diagnostic techniques to gain widespread adoption in ecological studies on natural enemy host range, they must provide information that is equivalent (or superior) to information obtained by conventional methods. Based on a large-scale case study, associations between Peristenus spp. and their mirid hosts were used to demonstrate the utility of molecular diagnostics in studies on parasitoid ecological host range; however, this approach can be extended to pre-release risk-assessment studies on other candidate biological control agents. Beyond agent identification, molecular diagnostics can facilitate and expedite pre- and post-release studies on the ecological host range of parasitoids, potential non-target effects, host-parasitoid associations and trophic interactions.