Variations in Response of Soybean Looper (Lepidoptera: Noctuidae) to Selected Insecticides in Louisiana

Abstract

Several strains of Pseudoplusia includens (Walker) (Lepidoptera: Noctuidae) were tested with permethrin, tralomethrin, lambda-cyhalothrin , acephate, and methomyl in laboratory tests. Permethrin was significantly less toxic to strains collected during 1987 (LD50’s 3.0 to 4.4 times higher) and 1988 (6.4 to 12.2 times higher) compared with a laboratory strain susceptible to permethrin. In response to methomyl, several field strains also had LD50’s that were significantly higher than those determined for the laboratory strain. No significant differences in the toxicity of tralomethrin or lambda-cyhalothrin were observed among strains and only one field strain was significantly less susceptible to acephate than the laboratory strain. In field trials during 1987 and 1988 in Tensas Parish (Paradise and St. Joseph) all treatments, and in Iberville Parish (St. Gabriel), all treatments except acephate (0.84 kg [Al]/ha) and sulprofos (0.51 kg [Al]/ha) significantly reduced numbers of larvae infesting the plots below numbers present in the untreated control plots. At one location (Tens as Parish, Louisiana), the standard rate of permethrin (0.11 kg [Al]/ha) was not as efficacious during 1987 (75-87% control) and 1988 (61-71% control) as it was during 1982 (97-99% control). None of the other pyrethroids (tralomethrin, cypermethrin, lambda-cyhalothrin , cyfluthrin), methomyl, thiodicarb, or acephate provided soybean looper control significantly greater than that observed with the permethrin (0.11 kg [AI]/ha) treatment.