Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

David J. Boethel


Field strains of soybean looper, Pseudoplusia includens (Walker), from Louisiana, Texas, and Puerto Rico were tested for permethrin synergism by piperonyl butoxide (PB) and S,S,S tributylphosphorotrithioate (DEF). Resistance was completely suppressed by 10 $\mu$g PB/larva in strains from Louisiana with 2.7 to 14.1-fold resistance. The Texas strain was 14.8-fold resistant and permethrin toxicity was increased 8.6-fold by PB. The Puerto Rico strain was highly resistant to permethrin (426.6-fold) and PB increased permethrin toxicity only 4.6 and 7.5-fold, respectively, at 10 and 20 $\mu$g/larva. No significant synergism resulted from DEF treatment in any of the strains tested. In field trials, efficacy of permethrin (0.11 kg AI/ha) plus PB (1.12 kg AI/ha) against soybean looper was significantly better than permethrin alone. Soybean looper larvae from a permethrin-resistant laboratory strain had comparable levels of resistance to $\alpha$-cyano pyrethroids but less resistance to the fluorinated phenyl alcohol pyrethroid tefluthrin and the non-ester pyrethroid BRC 429. Toxicity of each pyrethroid was increased by PB. Mixed-function oxidase activity was significantly higher in the resistant strain than in a susceptible laboratory strain and a non-selected strain. Penetration of $\sp{14}$C-cypermethrin was significantly decreased by PB, but no difference in cypermethrin metabolism was detected. The inheritance of permethrin resistance in the resistant laboratory strain was characterized by crosses with the susceptible strain. Resistance appeared to be inherited as a codominant trait (degree of dominance = 0.25, 95% C. L. = 0.18-0.32). Backcrossing to the susceptible strain indicated that $>$1 gene was involved in permethrin resistance. Several soybean looper strains were reared on artificial diet, soybean foliage, and cotton foliage and tested for permethrin tolerance. Larvae reared on cotton were significantly more tolerant to permethrin than those reared on artificial diet. Larvae reared on cotton developed more slowly than those reared on soybean, but larvae and pupae tended to attain greater weights when reared on cotton and survival was no different than on soybean.