Resistance monitoring of field populations of the corn borers Sesamia nonagrioides and Ostrinia nubilalis after 5 years of Bt maize cultivation in Spain

Abstract

Approximately 22 000 hectares (5% of the total maize growing area) of transgenic maize expressing the Cry1Ab toxin from Bacillus thuringiensis (Bt maize) have been planted annually in Spain since 1998. Changes in the susceptibility to Cry1Ab of Spanish populations of the Mediterranean corn borer (MCB), Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae), and the European corn borer (ECB), Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae), were assessed by annual monitoring on Bt maize fields. No increase in resistance was detected in the MCB populations from Ebro, Albacete, and Badajoz, nor in the ECB populations from Ebro and Badajoz during the period 1999-2002. The susceptibility of the MCB population from Madrid fluctuated from year to year, but a gradual trend towards higher levels of tolerance was not observed. Laboratory selection assays for eight generations yielded selected strains of MCB and ECB that were 21-and 10-fold significantly more tolerant to Cry1Ab than the corresponding unselected strains, respectively. Nevertheless, none of the fieldcollected or laboratory-selected larvae were able to survive on Bt maize. Considering these data, no consistent shifts in susceptibility were found for Spanish populations of MCB nor ECB after 5 years of Bt maize cultivation, but systematic field monitoring needs to be continued.

How can specific market demand for non-GM maize affect the profitability of Bt and conventional maize? A case study for the middle Ebro Valley, Spain

“…The chemical control of these two species is particularly difficult since insecticide sprays are only effective during the short period which elapses between the eggs hatching and the larvae boring into stems (Farinós et al, 2004;Agustí et al, 2005). Insect resistant (Bt) maize (Zea mays L. line MON810) can effectively control these two main pests and therefore reduce the yield losses associated with them (Demont & Tollens, 2004).…”

Opinion of the Scientific Panel on genetically modified organisms [GMO] related to the notification for the placing on the market of insect resistant genetically modified maize Bt11, for cultivation, feed and industrial processing

“…This could have several consequences including the use of alternative phytosanitary measures to control the pest including the use of insecticides other than Bt toxins. The Panel agrees that the likelihood of occurrence is low since under field conditions and several years of cultivation no resistance has been reported (Farinós et al, 2004). However, cultivation of Bt maize in Europe is currently at small scale and limited to few geographic regions and thus it is difficult to predict future responses of corn borer populations in Europe.…”

“…Up to now, resistant Ostrinia nubilalis or Sesamia nonagrioides have not been found in fields in the US or in Europe (Evans, 2002;Tabashnik et al, 2003;Bourguet et al, 2003;Farinós et al, 2004). Although laboratory tests showed that corn borer populations are capable of developing some degree of tolerance to the Cry1Ab protein (Huang et al, 2002), laboratory selection and F2 screening to generate highly resistant O. nubilalis strains have failed so far (Bourguet, 2004).…”

Opinion of the Scientific Panel on genetically modified organisms [GMO] related to the safeguard clause invoked by Greece according to Article 23 of Directive 2001/18/EC and to Article 18 of Directive 2002/53/EC

“…This implies that recessive resistance alleles are rare in European populations and the frequency of resistance alleles are below 1 x 10 -3 . Up to now, resistant Ostrinia nubilalis or Sesamia nonagrioides have not been found in fields in the US or in Europe (Evans, 2002;Tabashnik et al, 2005;Bourguet et al, 2002;Farinós et al, 2004) or in Spain (Eizaguirre et al, 2006). Although laboratory tests have shown that Ostrinia nubilalis populations are capable of developing some degree of tolerance to the CRY1Ab protein, laboratory selection and F2 screening to generate highly resistant Ostrinia nubilalis strains have failed so far (Bourguet, 2002).…”