COMPARATIVE TOXICITY OF THREE NOVEL BIOTIC COMPOUNDS, SPINOSAD PYRIDALYL AND RADICAL IN RELATIVE TO A CONVENTIONAL INSECTICIDE, LANNATE AGAINST THE FIELD AND LABORATORY STRAIN OF THE SECOND AND FOURTH INSTARS LARVAE OF COTTON LEAFWORM, Spodoptera littoralis (BOISD.)

Abstract

The toxic activity of three novel compounds (Pyridalyl, Radical, Spinosad) and conventional insecticide (Lannate) against the second and fourth instars of the lab and field strains of Spodoptera littoralis were evaluated under laboratory conditions. The obtained 2nd and 4th instar larvae of the field and lab strains were fed for 48h on castor leaves, Ricinus communis were dipped for 15 seconds in series of concentrations of each tested compounds to determine the LC50 values. Radical was the most toxic one against both of 2nd and 4th instar larvae of the susceptible and resistance strains. The LC50 values were 1.1, 2.7 and 1.95, 4.4 ppm for both second and fourth instar larvae of the two susceptible and resistance strains, respectively While, Pyridalyl was the second one, the LC50 values were 1.8, 5 and 6.2, 9.4 ppm for the two instars of both strains, respectively. Whereas, Lannate was the third one, its LC50 values were 3.9, 6 and 11, 19 ppm of both instars for of both strains, respectively. While Spinosad was the fourth one, its LC50 values were 21, 62.5 and 31.3 and 130 ppm of both instars for both strains, respectively. The biological activities of larvae were affected with the treatment of the second and fourth instars of both lab and field strains with the four tested compounds. The effect varied according to the strain, larval instar and tested compound, therefore, the larval treatment for both instars of the both strains with the four tested compounds caused highly significantly effect led to pupation and adult emergence percentages decrease at the tested four treatments. While, Pyridalyl treatment had the highest effect in larval duration, pupal and adult malformations increase; adult fecundity, fertility and longevity decrease in case of larval treatment of the two instars of both strains with this compound and it had the highest effect in pupal duration increase and weight decrease in case of treatment of the second instar of the field strain with this compound and it was effective against the sex ratios, the males increase and females decrease, as respect to control, with the treatment of fourth instar of lab strain with it. Whereas, Radical had the greatest effect on adult fecundity and fertility with fourth instar treatment of field strain with it. Also, it was effective against the pupal weight with the treated second instar of field strain and it had the highest effect on larval duration and adult malformations in case of the treatment of the second and fourth instars of lab strain with it and it had an adversely effect on the sex ratio (it caused males decrease and females increase) with the treatment of fourth instar of field strain with it. However, Spinosad had the highest effect on both adult fecundity and fertility with the treated fourth instar of field strain and it was the effect on adult malformations with the treatment of both instars of lab strain with it and affect the sex ratio, lead to males increase and females decrease with the treatment of fourth instar of lab strain with it. While, Lannate, had the highest effect on pupal malformations with the larval treatment of both instars of both strains with it and it was effective on pupal weight and adult malformations with the treatment of either second or second and fourth instar together of field strain with it also, it was effective on adult fecundity, fertility and longevity with the treated fourth instar of field strain and it had the highest effect on larval duration with the treatment of the fourth instar of the lab strain with it.