Cross-resistance of the diamondback moth indicates altered interactions with domain II of Bacillus thuringiensis toxins

Abstract

We compared responses to six insecticidal crystal proteins from Bacillus thuringiensis by a Cry1A-resistant strain (NO-QA) and a susceptible strain (LAB-P) of the diamondback moth, Plutella xylostella. The resistant strain showed >100-fold cross-resistance to Cry1J and to H04, a hybrid with domains I and II of Cry1Ab and domain III of Cry1C. Cross-resistance was sixfold to Cry1Bb and threefold to Cry1D. The potency of Cry1I did not differ significantly between the resistant and susceptible strains. Cry2B did not kill resistant or susceptible larvae. By combining these new data with previously published results, we classified responses to 14 insecticidal crystal proteins by strains NO-QA and LAB-P. NO-QA showed high levels of resistance to Cry1Aa, Cry1Ab, and Cry1Ac and high levels of cross-resistance to Cry1F, Cry1J, and H04. Cross-resistance was low or nil to Cry1Ba, Cry1Bb, Cry1C, Cry1D, Cry1I, and Cry2A. Cry1E and Cry2B showed little or no toxicity to susceptible or resistant larvae. In dendrograms based on levels of amino acid sequence similarity among proteins, Cry1F and Cry1J clustered together with Cry1A proteins for domain II, but not for domain I or III. High levels of cross-resistance to Cry1Ab-Cry1C hybrid H04 show that although Cry1C is toxic to NO-QA, domain III of Cry1C is not sufficient to restore toxicity when it is combined with domains I and II of Cry1Ab. Thus, diamondback moth strain NO-QA cross-resistance extends beyond the Cry1A family of proteins to at least two other families that exhibit high levels of amino sequence similarity with Cry1A in domain II (Cry1F and Cry1J) and to a protein that is identical to Cry1Ab in domain II (H04). The results of this study imply that resistance to Cry1A alters interactions between the insect and domain II.

Fishing for New Bt Receptors in Diamondback Moth

“…We first confirmed the susceptibility of the DBM strain 'Fuzhou' to three Lepidoptera-specific Bt toxins, Cry1Ac, Cry1Ab, and Cry1Bd by determining the concentration of the toxin that was lethal to 50% of the DBM (LC50). The LC50s of Cry1Ac, Cry1Ab, and Cry1Bd against the third larvae of this strain were 4.35 mg/L, 0.49 mg/L, and 0.05 mg/L, respectively, indicating that the Fuzhou strain is highly susceptible to Cry1Ac, Cry1Ab, and Cry1Bd, as reported previously [13,[25][26][27][28][29].…”

“…Some proteins also bound specifically to the Cry1Ac and Cry1Ab toxins, and each toxin captured several proteins in particular ( Figure 1, Supplemental Closer attention was paid to the proteins captured by Cry1Bd. This Cry toxin has the greatest potential to be used against DBM because the field population of this insect has evolved cross-resistance to four Bt toxins including Cry1Ac and Cry1Ab, but remains highly susceptible to Cry1Bd [13,25,[27][28][29]35]. Therefore, if Cry1Bd is to be used to control this pest, it is important to investigate potential Cry1Bd receptors [36,37].…”

“…The diamondback moth (DBM) Plutella xylostella (Lepidoptera: Plutellidae) causes US $4-5 billion in annual management costs [10] and is the first insect that was reported to have evolved resistance to Bt toxins in open fields [11]. The DBM resistance phenotype involves reduced binding of toxins to the brush border membrane cell proteins, a trait that is inherited in a recessive manner but which achieves high resistance levels [12,13]. Multiple Bt toxin receptors have been identified in lepidopteran insects [14].…”

Monitoring of resistance for the diamondback moth to Bacillus thuringiensis Cry1Ac and Cry1Ba toxins and a Bt commercial formulation

“…Tabashnik et al (1996) reported resistance to Cry1Ba had low or no levels of cross-resistance to other crystal proteins, such as Cry1Aa, Cry1Ab, Cry1Ac, Cry1Fa, Cry1Ja. Cry1A-resistant strain (NO-QA) of the diamondback moth showed high levels of resistance to Cry1Aa, Cry1Ab and Cry1Ac and low or no levels of cross-resistance to Cry1Ba (Tabashnik et al 1996). Rang et al (2004) reported that Cry1Ab and Cry1Ac in Spodoptera frugiperda, competed for the same binding site, whereas Cry1Ba and Cry1Ca competed for different binding sites.…”

Inheritance of Bacillus thuringiensis Cry1C resistance in Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae)

“…Among them, resistance of the cereal stem borer, Busseola fusca, in South Africa and fall armyworm, Spodoptera frugiperda, in Puerto Rico, to Bt corn producing either Cry1Ab (Kruger et al 2009) or Cry1F (Matten et al 2008), respectively, were studied. Also studied were the pink bollworm pest, Pectinophora gossypiella, in India (Bagla 2010), cotton bollworm, Helicoverpa zea, in the USA (Luttrell et al 2004;Tabashnik et al 2008Tabashnik et al , 2009) and diamondback moth, Plutella xylostella, in the USA (Tabashnik et al 1996;Cao et al 1999). Liu et al (2000) studied binding, toxicity and cross-resistance of Bt Cry1C in diamondback moth and bollworm, Helicoverpa punctigera, in Australia (Downes et al 2010) on development of resistance to Bt cotton producing Cry1Ac and Cry2Ab.…”