BIOLOGICAL FITNESS OF CULEX-QUINQUEFASCIATUS (DIPTERA, CULICIDAE) SUSCEPTIBLE AND RESISTANT TO BACILLUS-SPHAERICUS

Biological fitness of laboratory and field-collected strains of southe rn house mosquito, Culex quinquefasciatus Say, susceptible and resista nt (37- and 31-fold upon selection) to the microbial agent, Bacillus s phaericus, were compared in the absence of B. sphaericus. Tile resista nt strains showed significantly lower fecundity and fertility but they had significantly higher survival rates than the susceptible strains. The preadult stages from females of resistant strains developed at sl ightly faster rates than those of the susceptible strains, which could result in a shorter generation time. However, lower fecundity was lik ely to lead to overall lower population growth rates than in the susce ptible strains. Data provided evidence that the resistant strains exhi bited fitness disadvantages in the absence of B. sphaericus. We sugges t that once resistance to B. sphaericus is detected in the field, its use should be discontinued until the mosquito population becomes susce ptible again because of the decline in number of resistant individuals . A strategy of resistance management by rotation of insecticides is d iscussed.