Monitoring der Resistenzentwicklung des Maiszünsler (Ostrinia nubilalis), Hübner) gegenüber Bt-Mais
Monitoring of European corn borer (Ostrinia nubilalis>, Hübner) resistance to Bt-corn
by Thomas Meise
Date of Examination:2003-11-06
Date of issue:2004-04-23
Advisor:Dr. G.-A Langenbruch
Referee:Prof. Dr. Matthias Schaefer
Referee:Prof. Dr. Stefan Vidal
Persistent Address:
http://dx.doi.org/10.53846/goediss-432
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Abstract
English
Goal of this thesis was to collect data about baseline susceptibility and resistance allele frequency of the Euopean corn borer (Ostrinia nubilalis, Lepidoptera: Pyralidae) in Germany and to discuss methods and results according to resistance monitoring. The baseline susceptibility (LC50) of corn borer populations was determined using different methods for up to 3 years (2000 - 2002). The populations originated from several regions of corn cultivation: Niedernberg, Halle, Hessisches Ried, Pocking, Oderbruch. Furthermore a lab population, called Darmstadt population, was used. The experiments were conducted with purified Cry1Ab-toxin produced by E. coli. Cry1Ab-protoxin was tested as well as trypsinized toxins. The measurement of the LC50 showed strong fluctuations within the same year for a single population and between different years for all populations. The fluctuations between measurements were larger than the differences between populations from different Bt-corn regions. The geographical and annual differences seem to be based on fluctuations in natural sensitivity of the populations, because the populations were not exposed to Bt-toxin selection in former years. It has to be concluded from the results presented here, that a large variability of Euopean corn borer (ECB) baseline sensitivity must be expected in case of a resistance monitoring in Germany. Differences in sensitivity of a factor 10 have to be considered as natural fluctuations and are not indicating differences in resistance. Comparable LC50 values were obtained using two different methods. Toxin was either mixed with food or directly applied to the surface. However, when applied to the food surface 10-times less toxin is needed. The frequency of resistance alleles can be determined by several methods. In the study presented here two methods were selected to determine the frequencies of resistance alleles occurring in two German populations: F2-screening and monitoring of resistant corn borers from Bt-cornfields. In the years 2000 and 2001, 398 ECB larvae of the Niedernberg population were collected randomly and tested for presence of resistance alleles using the F2-screening. A resistance allele was not found. Using an error probability of 5 %, the confidence interval for the resistance allele frequency ranges between 0 and 4.2 x 10-3. Using the monitoring method about 204.942 Mon810 Bt-corn plants of the regions Oderbruch and Halle were checked for surviving corn borer larvae in 2001. The collected larvae were tested for resistance using biotests. Again, no resistance was found. A resistance allele frequency higher than 4.8 x 10-3 can be excluded for both regions by the monitoring of resistance corn borers on Bt-cornfields. We used a statistical model to compare the efficiency of the F2-screening method with the resistance monitoring method on Bt-cornfields, considering the amount of non-transgenic plants on a Bt-cornfield as well as the costs for the two different methods. At a resistance allele frequency of 10-3 and a pollution of less than 0.001 %, the F2-screening on non-Bt-cornfields is more effective to determine frequency of resistance than the monitoring of resistance in Bt-cornfields.
Keywords: European corn borer; Ostrinia nubilalis; Bacillus thuringiensis; Cry1Ab; Bt-corn; insecticide resistance; resistance monitoring; baseline susceptibility; F2-Screening; in-field screen; allel frequency; LC50
Other Languages
Ziel dieser Arbeit war es, Daten zur Basisempfindlichkeit und zur Resistenzhäufigkeit der Maiszünsler (Ostrinia nubilalis, Hübner) in Deutschland zu erheben und die Methoden und Ergebnisse in Hinblick auf ein Resistenzmonitoring zu diskutieren. Die Basisempfindlichkeit (LC50) wurde mit verschiedenen Methoden und zum Teil für drei Jahre für Maiszünslerpopulationen der Anbaugebiete Niedernberg, Halle, Hessisches Ried, Pocking und Oderbruch ermittelt. Zusätzlich wurde ein Laborstamm als mögliche Referenz in die Untersuchungen miteinbezogen. Die Untersuchungen wurden mit gereinigtem Cry1Ab-Toxin, das in E. coli produziert wurde, durchgeführt. Sowohl das Cry1Ab-Protoxin als auch trypsinisierte Toxine wurden verwendet. Die Resistenzallelfrequenz kann durch mehrere Methoden ermittelt werden. In dieser Arbeit wurden das F2-Screening und das Monitoring resistenter Maiszünsler auf Bt-Maisflächen verwendet um die Resistenzhäufigkeiten zweier Populationen in Deutschland zu ermitteln. Die hier vorgestellten Ergebnisse können für die Planung und Durchführung von Resistenzmanagement-Programmen in Deutschland eingesetzt werden. Sie sind erste Schritte auf dem Weg zu einem Resistenzmonitoring des Maiszünslers.
Schlagwörter: Maiszünsler; Ostrinia nubilalis; Bacillus thuringiensis; Cry1Ab; Bt-Mais; Insektizidresistenz; Resistenzmonitoring; Basisempfindlichkeit; F2-Screening; Allelfrequenz; LC50; 570 Biowissenschaften; Biologie
