SIGNIFICANCE OF PENETRATION AND METABOLISM ON TOPICAL TOXICITY OF DIFLUBENZURON IN SPODOPTERA-LITTORALIS AND SPODOPTERA-EXIGUA

Toxicity assays indicated that when diflubenzuron (DFB) was topically applied on larvae of the Egyptian cotton leafworm, Spodoptera littoral is (Boisduval), and the beet armyworm, Spodoptera exigua (Hubner), est imated LD50 values were similar, reaching 0.47 and 0.44 ng/larva, resp ectively. This study evaluated the importance of the rate of uptake an d excretion, and of enzymatic metabolism in building up an insecticida l toxicity after topical application on the insect cuticle in both spe cies. In general, penetration of DFB in S. littoralis was about 2-fold higher than in S. exigua, whereas metabolic breakdown was of minor im portance in S. littoralis as compared with S. exigua. The current data indicate the importance of cuticle penetration and discuss that extra polation from oral feeding toxicity results to topical toxicity data s hould be evaluated with caution, especially for insect growth regulato rs used in integrated pest management.