The European corn borer (Ostrinia nubilalis, Hbn.), its susceptibility to the Bt-toxin Cry1F, its pheromone races and its gene flow in Europe in view of an insect resistance management
Year: 2010
Type: dissertation
Abstract: One of the most promising and effective method for a control of the maize pest, Ostrinia nubilalis (European corn borer; „ECB“), is the cultivation of Bt-maize, which expresses lepidoteran-specific toxins. For a sustainable use of this technology an insect resistance management (IRM) is required to delay resistance development of the target pest, because in the past insects have developed resistance to all major classes of chemical insecticides. As a consequence of the increasing cultivation of Bt-plants since 1996 in the USA and since 1998 in Europe (Spain) it is suspected that resistance against several Bt-toxins is likely. The most promising strategy to recognize and counter such a development seems to be a monitoring of the baseline susceptibility of the target pest and the implementation of the high-dose/refuge (HDR) strategy, which entails the cultivation of Bt-maize expressing high toxin concentrations in combination with setting up refuges. For the HDR strategy to be effective, further requirements (low incidence of resistance, recessive inheritance of resistance) are essential. Baseline studies are an efficient approach to observe a development of resistance world-wide. Bt-maize producing the Cry1F protein was commercially available in 2003 in the USA and is pending regulatory approval in the EU. Therefore, in this work the baseline susceptibility of ECB to Cry1F prior to a widespread commercial use of Cry1F Bt-maize in Europe and the USA was established for 11 European (EU) and for 24 North American (US) populations of O. nubilalis. The results showed small, but meaningless differences (for the HDR strategy) in the observed susceptibility between the European and North American ECB and among the various populations within each continent. The source of the differences in susceptibility between EU and US borers is most likely due to the natural variation, differentiation in the test protocols applied, or the use of different toxin batches for different bioassays. For a successful implementation of the high-dose/refuge (HDR) strategy for resistance management reliable data are needed on aspects of ECB genetics and biology. Any resistant insect emerging from the Bt-crop should be able to mate with susceptible adults emerging from the refuge. The resulting offspring will be heterozygous in terms of their resistance genes, and thus susceptible to Bt. Therefore the population structure of O. nubilalis regarding the different sex pheromone races, their spatial distribution and their association with specific host plants was investigated. GC-analysis was used to assess the distribution of the two pheromone races of the ECB in several European countries and from different host plants. The results indicated that ECB individuals from maize populations in Italy and Greece were predominantly E-race, whereas those from Germany, France, Spain, Serbia and Croatia were mostly Z-race, including a German hop population. In a German mugwort population all three pheromone types in equal parts were present. Nearly all populations contained a considerable number of hybrids (EZ) except for Pola (Serbia) and Poitiers (France) with pure Z-race. After race-determination, Tpi (Triose-phosphate-isomerase) allozyme analyses were performed with males and with GC-analysed females. The obtained results indicated that the Tpi locus cannot be reliably used as a marker for the different pheromone races as described previously. Allozyme electrophoresis was used to examine the genetic variability of the ECB for surveying the sustainability of Bt-maize, because the strategy for delaying resistance to Bt-toxins requires high gene flow between ECB from transgenic and refuge plants. ECB samples collected from 22 locations in Europe and one from Asia (Georgia) were investigated for their allozyme variation at five loci, which were known to be polymorphic in O. nubilalis. All populations were collected from maize, except one which was collected on hop. The overall genetic differentiation was low, suggesting a high and homogeneous gene flow. No obvious genetic differences could be detected between the ECB population on hop and those collected on maize, nor between the two pheromone race populations collected on maize. The overall results of this study support strongly the application of the HDR strategy to counteract and delay a pest resistance development of ECB in Europe and the US. The risk of resistance development is real but it can be managed.
Source: RWTH Publications (RWTH Aachen)
Authors: Claudia Gaspers, Ingolf Schuphan
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2209298674