Use of Bacillus thuringiensis Toxins for Control of the Cotton Pest Earias insulana (Boisd.) (Lepidoptera: Noctuidae)

Abstract

Thirteen of the most common lepidopteran-specific Cry proteins of Bacillus thuringiensis have been tested for their efficacy against newly hatched larvae of two populations of the spiny bollworm, Earias insulana. At a concentration of 100 g of toxin per milliliter of artificial diet, six Cry toxins (Cry1Ca, Cry1Ea, Cry1Fa, Cry1Ja, Cry2Aa, and Cry2Ab) were not toxic at all. Cry1Aa, Cry1Ja, and Cry2Aa did not cause mortality but caused significant inhibition of growth. The other Cry toxins (Cry1Ab, Cry1Ac, Cry1Ba, Cry1Da, Cry1Ia, and Cry9Ca) were toxic to E. insulana larvae. The 50% lethal concentration values of these toxins ranged from 0.39 to 21.13 g/ml (for Cry9Ca and Cry1Ia, respectively) for an E. insulana laboratory colony originating from Egypt and from 0.20 to 4.25 g/ml (for Cry9Ca and Cry1Da, respectively) for a laboratory colony originating from Spain. The relative potencies of the toxins in the population from Egypt were highest for Cry9Ca and Cry1Ab, and they were both significantly more toxic than Cry1Ac and Cry1Ba, followed by Cry1Da and finally Cry1Ia. In the population from Spain, Cry9Ca was the most toxic, followed in decreasing order by Cry1Ac and Cry1Ba, and the least toxic was Cry1Da. Binding experiments were performed to test whether the toxic Cry proteins shared binding sites in this insect.125 I-labeled Cry1Ac and Cry1Ab and biotinylated Cry1Ba, Cry1Ia, and Cry9Ca showed specific binding to the brush border membrane vesicles from E. insulana. Competition binding experiments among these toxins showed that only Cry1Ab and Cry1Ac competed for the same binding sites, indicating a high possibility that this insect may develop cross-resistance to Cry1Ab upon exposure to Cry1Ac transgenic cotton but not to the other toxins tested.

Molecular and Insecticidal Characterization of a Cry1I Protein Toxic to Insects of the Families Noctuidae, Tortricidae, Plutellidae, and Chrysomelidae

“…Cry1Ac could displace Cry1Ab binding in E. insulana (Fig. 5A, lane 5), in agreement with previous data (20). Taken together, these results indicate that Cry1Ia7 binds to sites different from those of Cry1Ab in both species.…”

Potential of the Bacillus thuringiensis Toxin Reservoir for the Control of Lobesia botrana (Lepidoptera: Tortricidae), a Major Pest of Grape Plants

“…Similarly, Cry1Ab was shown not to share binding sites with biotinylated Cry1Ia and Cry9Ca in L. botrana BBMV. The fact that Cry1Ia did not share common binding sites with Cry1A toxins has recently been reported for the cotton pest Earias insulana (13). Cry2A toxin-specific binding could not be demonstrated in this study by using the same conditions as those used for Cry1A toxins, but this is not surprising, as these toxins seem to have different modes of action (5,18,19).…”

Transgenic Bt Cotton: Effects on Target and Non-Target Insect Diversity

“…It is an important pest of cotton in Indo-Pak subcontinent and cause damage to fruiting bodies and shedding of squares, flowers and bolls [102,103]. Although, the primary target of transgenic Bt cotton is to control cotton bollworm, H. armigera but it also has a significant impact on other bollworm species, including Earias insulana & E. vittella.…”