The accidental importation of plant pathogens in or on the bodies of parasitoids imported as natural enemies has been raised as a potential risk of classical biological control projects involving insects that serve as vectors of plant diseases. During quarantine evaluation of two parasitoids, Tamarixia radiata and Diaphorencyrtus aligarhensis , imported for classical biological control of Asian citrus psylla Diaphorina citri in Florida, we were asked to determine that these parasitoids were free of the causal agent of Asian greening disease, the bacterium Liberobacter asiaticum . Preliminary tests using allele-specific polymerase chain reaction (Standard PCR) suggested the assays were prone to false negatives. Another PCR protocol, Long PCR, previously was shown to be more reliable than Standard PCR when screening insects for another bacterium ( Wolbachia ). The sensitivity of Long and Standard PCR protocols was compared using plasmid DNA containing two DNA fragments from the greening disease agent or plasmid mixed with DNA extracted from host plants, psyllids or parasitoids. Results indicated that inhibitors of the PCR were present in both plant and insect DNA, making the Standard PCR relatively insensitive and allowing high levels of false negatives. Long PCR yielded consistent results and was orders of magnitude more sensitive than the Standard PCR. As few as 100 copies of plasmid mixed with either plant or insect DNA consistently could be detected. Long PCR assays conducted on the parasitoids, their psyllid hosts, or their host plants failed to produce any positives, indicating that release of these two parasitoids should elicit little concern that greening bacteria would be introduced accidentally into Florida through this classical biological control program.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA