Laboratory and Field Evaluation of Bacillus sphaericus as a Mosquito Control Agent1

Abstract

Bacillus sphaericus Neide strain 1593–4 was found to be more virulent against the southern house mosquito, Culex quinquefasciatus Say, and possessed longer residual activity than strain SSII-1 in pond tests at Fresno, CA. Furter testing of strain 1593-4 provided excellent control of a natural population of Culex tarsalis Coquillett in Kern County, CA, at 10⁴ cells/ml. Infectivity of the bacterium on a mixed population of C. tarsalis and southern house mosquito was decreased in a treatment of a dairy drain. A WP formulation of 1593-4 improved handling of the material and resulted in operational control of C. tarsalis at 0.84 kg/ha (7.6×10³ spores/ml). Effective control of a mixed population of Aedes melanimon Dyar and A. nigramaculis (Ludlow) was not obtained at 10⁴ cells/ml in 0.02-ha pasture plots, although laboratory tests showed A. nigromaculis had a high susceptibility to the bacterium compared to other Aedes spp. A field test of strain 1593-4 showed no deleterious effect on nontargets at 10⁵ cells/ml. Fry of the mosquito fish, Gambusia affinis affinis (Baird and Girard), showed no adverse effect at 5 × 10⁴ spores/ml of 1593-4 WP.