PYRETHROID RESISTANCE LEVELS IN 2 GENERATIONS OF SOYBEAN LOOPER (LEPIDOPTERA, NOCTUIDAE) ON SOYBEAN IN MISSISSIPPI

Resistance to permethrin in soybean looper, Pseudoplusia includens (Wa lker) (Lepidoptera: Noctuidae), larvae from generations one and two on soybean, Glycine max (L.) Merrill, was monitored in the central Delta area (Holmes County) of Mississippi in 1992. Dose responses were dete rmined by topical treatment of third instars. Populations of first- an d second-generation soybean looper had LD(50)s (95% confidence limits [CL] expressed as micrograms of insecticide per larva) of 0.0028 (0.00 18-0.0040) and 0.0096 (0.0050-0.0154), respectively, which were signif icantly higher than the LD(50) (CL) of the susceptible laboratory stra in (0.0002 [0.0001-0.0003]). Resistance level in the second generation was 3.4-fold higher than that in the first generation. Similar data w ere obtained by Portillo et al. (1993) in recording 3.3- and 2.2-fold higher soybean looper resistance levels in second-generation than in f irst-generation soybean looper in 1989 and 1991, respectively. These d ata corroborate earlier reports that levels of soybean looper resistan ce to pyrethroid insecticides significantly increased in cotton-soybea n production areas as the crop growing season progressed. It appears t hat mid-season pyrethroid insecticide applications on cotton increase selection pressure for pyrethroid resistance in soybean looper populat ions in cotton-soybean agroecosystems.