Submitted to: Journal of Insect Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/16/2008
Publication Date: 10/23/2008
Publication URL: insectscience.org/8.69
Citation: Krumm, J.T., Hunt, T.E., Skoda, S.R., Hein, G.L., Clark, P.L., Lee, D.J., Foster, J.E. 2008. Genetic variability of the European corn borer, Ostrinia nubilalis, suggests gene flow between populations in the Midwestern United States. Journal of Insect Science. 8:69. Interpretive Summary: European corn borers (ECB) were introduced to the U.S. in the early 20th century, have spread through most of the country and are among the most important pests in the U.S. Corn Belt states. For a recently introduced insect it is reasonable to expect little genetic variability, but this is not the case in ECB. Developing effective and durable control tactics for a pest includes understanding the genetic variability of the pest. We used amplified fragment length polymorphisms (AFLP), a robust molecular genetic technique, to determine genetic variability in 18 sub-populations of ECB. Samples were collected from corn fields in 8 states in the upper Midwest and, for comparison, from rice fields in Louisiana; populations were compared to each other and based on region of collection (north, south, east or west). Results from AFLP were successful in displaying the ‘relatedness’ of samples, indicating that molecular markers may be useful for this purpose. We found more genetic variability within populations than between populations. Modest genetic differences were detected between northern and southern samples and may reflect the large climate differences and reduced mating season. These results indicate the probability of gene flow (mixing of the populations) and therefore support for current requirements of refugia corn planting in Bt-corn management. But high gene flow also indicates that if ECB were to evolve resistance to Bt-corn, quick action would be necessary to defer the rapid spread of the gene for resistance.
Technical Abstract: Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) is a widely distributed and serious economic pest to corn production in the U.S. Genetic variability of O. nubilalis was studied in 18 sub-populations in the upper Midwestern United States using amplified fragment length polymorphism (AFLP). The relatively low GST values indicate that more variation exists within populations than between populations. High gene flow (Nm) values were indicated across the entire O. nubilalis population; the lowest degree of gene flow was in the northern samples (Nm = 1.96) and the highest degree of gene flow was in the southern samples (Nm = 2.77). The differences observed in the respective regions (north vs. south) may possibly be explained by the voltinism patterns (univoltine vs. multivoltine, respectively) of O. nubilalis: southern multivoltine populations have opportunities for multiple matings for the duration of the year, further mixing alleles. AMOVA results also indicated that most of the genetic variation was within sub-populations (' 81% of total variation); less variation ('13%) was detected among populations within each of the three regions as designated for this study. However, the most striking and unexpected result was the low percentage of variation between all groups ('6%), further supporting implications of a high degree of gene flow. These results provide support for current requirements of refugia corn planting in Bt-corn management. But, these results indicate that if resistance to Bt were to evolve in O. nubilalis, quick action would be necessary to defer the rapid spread of the gene for resistance.