RESISTANCE IN A LABORATORY POPULATION OF CULEX-QUINQUEFASCIATUS (DIPTERA, CULICIDAE) TO BACILLUS-SPHAERICUS BINARY TOXIN IS DUE TO A CHANGEIN THE RECEPTOR ON MIDGUT BRUSH-BORDER MEMBRANES

Direct binding experiments with isolated brush border membrane fractio ns (BBMF) from larvae of a susceptible laboratory strain of Culex quin quefasciatus Say, indicated the presence of a single class of Bacillus sphaericus binary toxin receptors. The dissociation constant (K-d) wa s approximately 11 nM and the maximum binding capacity (B-max) approxi mately 8 pmol/mg BBMF protein. Similar binding experiments with a fiel d population of C. quinquefasciatus that had been selected in the labo ratory to more than 100000-fold resistance to B. sphaericus binary tox in failed to reveal the presence of any specific binding. Thus this re sistant strain had lost the functional receptor for B. sphaericus toxi n. The binding characteristics of BBMF from the F-1 larval progeny (su sceptible femalesXresistant males) were very close to those of the par ental susceptible strain, consistent with the resistance being recessi ve.