Frequency of hybridization between Ostrinia nubilalis E-and Z-pheromone races in regions of sympatry within the United States

Authors: Coates, Brad; JOHNSON, HOLLY - University Of Delaware; KIM, KYUNG SEOK - Seoul National University; Hellmich Ii, Richard; Abel, Craig; MASON, CHARLES - University Of Delaware; Sappington, Thomas

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2013
Publication Date: 6/24/2013
Publication URL: http://onlinelibrary.wiley.com/doi/10.1002/ece3.639/full
Citation: Coates, B.S., Johnson, H., Kim, K., Hellmich II, R.L., Abel, C.A., Mason, C., Sappington, T.W. 2013. Frequency of hybridization between Ostrinia nubilalis E-and Z-pheromone races in regions of sympatry within the United States. Ecology and Evolution. 3(8):2459-2470.

Interpretive Summary: The European corn borer can cause damage to crop plants that results in significant economic loss to producers, but has recently been controlled by planting of transgenic corn that express toxins derived from the soil bacterium, Bacillus thuringiensis. Random gene flow within European corn borer populations is important for the success of refuge strategies designed to delay the accumulation of resistance to Bacillus thuringiensis toxins. Two types of ECB are present in the United States, and are called E- and Z-races. We developed the first genetic marker that allowed for the differentiation of E- and Z-race ECB within populations. Results indicated that a relatively high frequency of mating occurs between these two types in corn growing regions of the United States, and suggest that gene flow occurs among E- and Z-race ECB. These results are important for the evaluation of refuge strategies in the United States, and impacts the management practices used by stakeholders to control feeding damage to crop plants.

Technical Abstract: Female European corn borer, Ostrinia nubilalis, produce and males respond to a sex pheromone blend with either E- or Z- 11-tetradecenyl acetate as the major component. E- and Z-race populations are sympatric in the Eastern United States, Southeastern Canada and the Mediterranean region of Europe. The E- and Z-pheromone races of O. nubilalis are models for incipient species formation, but hybridization frequencies within natural populations remain obscure due to lack of a high throughput phenotyping method. Pheromone gland fatty-acyl reductase, the product of the pgfar gene, controls production of 11-tetradecenyl acetate stereoisomers. We identified three single nucleotide polymorphism (SNP) markers within pgfar that are differentially fixed between E- and Z-race females, and that are = 98.2% correlated with female pheromone ratios measured by gas chromatography. Genotypic data from locations in the United States demonstrated that pgfar-z alleles were fixed within historically allopatric Z-pheromone race populations in the Midwest, and that hybrid frequency ranged from 0.00 to 0.42 at 11 sites with sympatric populations of the two races in the Eastern United States (mean hybridization frequency or heterozygosity (HO) = 0.226 ± 0.279). Estimates of hybridization between the E- and Z-races are important for understanding the dynamics involved in maintaining race integrity, and are consistent with previous estimates of low levels of genetic divergence between E- and Z-races and the presence of only weak pre-zygotic mating barriers.