Binding studies using 125 I-Cry1Ac and biotinylated Cry1Fa toxins indicate the occurrence of a common receptor for Cry1Ac, Cry1Fa, and Cry1Ja in Helicoverpa armigera, Helicoverpa zea, and Spodoptera exigua. Our results, along with previous binding data and the observed cases of cross-resistance, suggest that this pattern seems to be widespread among lepidopteran species.
Aims:The current work aimed to study the presence of b-exotoxin by high-performance liquid chromatography (HPLC) in supernatant¯uids from ®nal whole cultures of the 69 type strains and 13 subtypes of Bacillus thuringiensis strains, as well as from some insecticidal strains.
Methods and Results:Results from HPLC and bioassays with Ephestia kuhniella (Lepidoptera Pyralidae) were compared. Type I b-exotoxin was only detected in type strains representing serotypes H1, H9 and H10a,10b. Discrepancies between HPLC and bioassays were found in H8a,8b and some insecticidal strains, which suggests the occurrence of another soluble toxin different from type I b-exotoxin, possibly type II b-exotoxin. Conclusions: This study shows the need to use bioassays to determine the presence of bexotoxin activity. However, HPLC is a fast and sensitive technique if only type I b-exotoxin is to be determined. The occurrence of b-exotoxin in a type strain does not imply production of this metabolite by other strains belonging to the same serovar. Signi®cance and Impact of the Study: These results complete the characterization of type strains belonging to
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