Cross‐resistance of Cry1Ab‐selected Asian corn borer to other Cry toxins

Abstract

The Asian corn borer, Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae), is the most important insect pest of maize in China. Despite the proven track record of biotech Bacillus thuringiensis (Bt) maize to provide an effective means to control lepidopteran pests such as the European corn borer Ostrinia nubilalis (Hübner), these crops have not been commercialized in China. However, Cry1Ab‐ and Cry1F‐expressing maize derived from genetic transformation events MON810 (Monsanto), Bt11 (Syngenta) and TC1507 (Pioneer, DuPont) as well as Cry1Ah‐, Cry1A‐ (a Cry1Ab/Cry1Ac hybrid toxin), and Cry1Ac‐, Cry1Ie‐expressing maize developed by the Chinese institutions have been shown to effectively suppress O. furnacalis in field trials. The development of resistance in target pests is a major threat to the use of Bt maize. A strain of O. furnacalis selected with Cry1Ab protein incorporated into artificial diet developed more than 100‐fold resistance to Cry1Ab after 35 generations of selection, and readily consumed Cry1Ab‐expressing maize silks. Although LC50s of the selected insect strain were not progressively increased, and even decreased in the following generations, these insects (ACB‐AbR) could survive on Cry1Ab‐expressing maize tissue after 51 generations of selection. In addition, susceptibility of ACB‐AbR to a number of other Bt toxins to which the selected strains had not previously been exposed, was significantly decreased. The highest level of cross‐resistance was observed with Cry1Ah (131‐fold), followed by Cry1Ac (36‐fold). A low level of cross‐resistance (6‐fold) to Cry1F was also detected. In contrast, ACB‐AbR was equally susceptible to Cry1Ie as the unselected control strain. These results indicate that the availability of multiple toxins could improve resistance management strategies, provided that the potential for cross‐resistance among toxins is not an issue.

Comparative binding of Cry1Ab and Cry1F Bacillus thuringiensis toxins to brush border membrane proteins from Ostrinia nubilalis, Ostrinia furnacalis and Diatraea saccharalis (Lepidoptera: Crambidae) midgut tissue

“…The present results also demonstrate that Cry1Ab and Cry1F have high affinity to different protein receptors, thus supporting the observation of low cross resistance levels from Cry1Ab to Cry1F in O. furnacalis and O. nubilalis (Siqueira et al, 2004a;Xu et al, 2010). Furthermore, it has been reported that Cry1Ab shares a low affinity receptor with Cry1F in O. nubilalis (Hua et al, 2001).…”

Identification of a New cry1I -Type Gene as a Candidate for Gene Pyramiding in Corn To Control Ostrinia Species Larvae

“…The levels of Cry1Ie2 toxicity to O. nubilalis neonates were comparable to those reported for the Cry1Ab (41,42) and Cry1Fa (5,40) toxins. This similar toxicity is also indirectly supported by reports of a lack of significant differences (based on overlapping confidence intervals) in Cry1Ie1, Cry1Ab, and Cry1Fa toxicity to O. furnacalis (14) and the same toxicity to Ostrinia species larvae observed for the Cry1Ie1 and Cry1Ie2 toxins in the present study. The new Cry1Ie2 toxin was expressed in E. coli cultures as a protoxin of 81 kDa, a molecular mass uniquely common to other Cry1I toxins (11,12).…”

“…These observations are in contrast to a previous report on Cry1Ia7 toxin activity against noctuid larvae (11) but in agreement with bioassay data on Cry1Ie toxins (12). High Cry1Ie activity against Ostrinia species explains why Cry1Ie1-expressing maize effectively suppressed O. furnacalis in field trials (14). Taken together, our bioassay data support a restricted range of Cry1Ie2 activity against lepidoptera yet high activity against key Ostrinia pest species.…”

“…Transgenic maize expressing Cry1Ie1 was shown to effectively control O. furnacalis in field trials and displayed toxicity to Cry1Ac-resistant Helicoverpa armigera (13). Furthermore, no cross-resistance to Cry1Ie was detected in a Cry1Ab-resistant strain of O. furnacalis (14) or a Cry1Ac-resistant strain of P. xylostella (15). Expression of the Cry1Ac and Cry1Ie1 toxins in transgenic tobacco produced greater activity against susceptible or Cry1Ac-resistant H. armigera than in plants producing a single toxin (16).…”

A single major QTL controls expression of larval Cry1F resistance trait in Ostrinia nubilalis (Lepidoptera: Crambidae) and is independent of midgut receptor genes

“…In contrast, interaction was shown between Cry1Ab and cadherin for both resistant and susceptible O. nubilalis (Siqueira et al 2006;Flannagan et al 2005). Despite the possibility that Cry1F and Cry1Ab toxins share receptor sites on O. nubilalis cad and apn1 proteins, the laboratory-selected Cry1Ab-resistant strains shows low cross-resistance to Cry1F toxin (Siqueria et al 2004) as did the O. furnicalis ACB-AbR strain (Xu et al 2010). Furthermore, cad and apn1 loci do not co-segregate with an O. nubilalis Cry1Ab trait from a colony that shows [2,500-fold increase in resistance (Coates et al 2008a), which that alleles at these loci do not contribute to larval Cry1Ab resistance traits.…”