Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/5/2013
Publication Date: 10/30/2013
Citation: Green, E., Almskaar, K., Sim, S., Arcella, T., Yee, W.L., Feder, J., Schwarz, D. 2013. Molecular species identification of cryptic apple and snowberry maggots (Diptera: Tephritidae) in Western and Central Washington. Environmental Entomology. 42(5):1100-1109. Interpretive Summary: The apple maggot fly is an important quarantine pest of apples in the Pacific Northwest of the U.S. The snowberry maggot fly is a non-pest but looks almost exactly like apple maggot fly. Molecular methods to identify the two species would be useful for pest management. Personnel at the Yakima Agricultural Research Laboratory in Wapato, WA, Western Washington University, and the University of Notre Dame determined ways to identify apple maggot fly and snowberry maggot fly using polymerase chain reaction (PCR) methods. Methods were adequate in most cases for distinguishing the two species, although hybridization between them appeared to occur in the wild and complicated analyses. Results are important because application of the PCR assay can immediately assist ongoing apple maggot monitoring to help protect U.S. apple exports.
Technical Abstract: In Washington state, identification of the quarantine apple pest Rhagoletis pomonella (Walsh) is complicated by the presence of the cryptic species R. zephyria Snow (Diptera: Tephritidae). Distinguishing the two flies is important because there is a zero tolerance policy for R. pomonella in apple production for export. Here, we attempt to distinguish the two species by scoring R. pomonella and R. zephyria populations from western and central Washington for a set of 11 nuclear markers, including four single nucleotide polymorphisms (SNPs) developed for rapid and inexpensive genotyping using Taqman© real-time qPCR. We show that the four SNPs may be adequate in most cases for distinguishing whether a fly originated from apple/black hawthorn (the two major host plants for R. pomonella representing an economic risk) versus snowberry (the major host for R. zephyria, and not a commercial threat). However, directional introgression of R. zephyria alleles into R. pomonella can complicate the identification of flies of mixed ancestry based only on the four SNPs. Moreover, this problem is more acute in the sensitive apple growing regions of central Washington where our results imply hybridization is common. Consequently, application of the four SNP qPCR assay can immediately assist ongoing apple maggot monitoring, while the development of additional genetic markers through next generation sequencing would be valuable for increasing confidence in species identification and for assessing the threat posed by hybridization as R. pomonella further spreads into the more arid apple growing regions of central Washington.