Strains of Culex quinquefasciatus Say, selected for resistance to 1, 2, 3, or 4 of the insecticidal toxins produced by the bacterium Bacillus thuringiensis subsp. israelensis Berliner, were tested with individual B. thuringiensis subsp. israelensis toxins, as well as combinations of toxins, to determine the pattern of the resulting resistance and cross-resistance. In each strain, except the Cq4AB (c. quinquefasciatus selected with CryIVA + CryIVB), resistance ratios at the LC93, were generally highest toward the strain's respective selecting toxin (s). The strain Cq4D, selected with CryIVD, demonstrated significant cross-resistance to CryIVA + CryIVB, and vice-versa. Selected strains also revealed resistance toward the component toxins present in their respective selecting mixture. For example, the Cq4ABDCytA strain, which was selected with all 4 of the naturally occurring insecticidal toxins in B. thuringiensis subsp. israelensis (CryIVA, CryIVB, CryIVD, CytA), revealed only a low level of resistance toward this mixture, whereas much higher levels of resistance were detected toward individual CryIV toxins as well as combinations of 2 or 3 CryIV toxins. All of the selected lines remained sensitive to the native 4-toxin mixture in B. thuringiensis subsp. israelensis, suggesting that the CytA toxin, which was present only in the 4-toxin mixture and differs in sequence and mode of action from the CryIV toxins. may play an important role in suppressing resistance to CryIV toxins.
Document Type: Research Article
Publication date: December 1, 1997
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Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.