Metabolism and excretion of leptophos and its phenol in S and R larvae of the Egyptian cotton leafworm.

The metabolism and excretion of leptophos, 0-(4-bromo-2,5 dichlorophenyl) 0-methyl phenylphosphonothioate, and its phenol, 4-bromo-2,5-dichlorophenol, were examined in susceptible (S) and leptophos resistant (R) strains of the Egyptian cotton leafworm Spodoptera littoralis (Boisd.). Leptophos injected into the larvae is converted in vivo into at least five chloroform-soluble and two water-soluble products. Minor qualitative differences were observed between S and R larvae. Quantitatively, the disappearance of leptophos was faster in R (t1/2 = 2.5 hr) than in S (t1/2 = 21.5 hr) larvae. A small amount of leptophos oxon (2 to 7%) was detected in S larvae, but none in R larvae. The major degradation product was the free phenol and its amount was relatively higher in R (17 to 22%) than in S (5 to 5%) larvae. After 24 hr, 25% of the injected leptophos was excreted unchanged by R larvae, whereas less amount (15%) was excreted by S larvae. However, the amount of excreted phenol, in free form, by S and R larvae was almost equal (5 to 8%). Following injection of the phenol derivative, its disappearance was faster in S (t1/2 = 36 min) than in R (t1/2 = 72 min) larvae, whereas phenol excretion, 24 hr after injection, was significantly higher by R (37%) than by S (9%) larvae.