Emamectin benzoate and spinetoram are two important and
promising new insecticides in caterpillar lepidoptera larvae/larvae
control. The toxicity of these compounds against larvae of cotton
leafworm (CLW), Spodoptera littoralis (Boisd.) was compared
using topical application and feeding techniques. The
persistence/residual efficacy under field conditions was also
investigated. Based on the LD50 values against 4th instar larvae,
emamectin benzoate proved to be better than spinetoram by 31516
fold. The LD50 values of emamectin benzoate, cypermethrin,
methomyl, chlorpyrifos, pyriproxyfen, profenofos, chlorpyrifosmethyl, abamectin, spinetoram, spinosad and imidacloprid were
0.0019, 0.0039, 0.03, 1.62, 3.13, 3.38, 4.00, 9.38, 59.88, 558.25
and 37384.38 µg a.i/ g larvae, respectively. The 3rd instar larvae
showed higher susceptibility toward emamectin benzoate than
spinetoram by 1551 and 41 times after 2 days post-treatment using
cotton and castor bean, respectively. Two days post- treatment, the
persistence of emamectin benzoate decreased gradually and
significantly. After spraying cotton, the mortality percentages were
98.00, 70.00, 36.67 and 0.00 % after 0, 3, 6 and 10 days,
respectively. However, the mortality % of this insecticide in castor
was 91.11, 93.33 and 0.00 % after 0, 3 and 6 days respectively. In
spinetoram, these percentages in cotton and castor were 96.67,
3.33, 3.33 and 0.00, 2.86, 0.00 after 0, 3 and 6 days. Our
investigation recommended that emamectin benzoate is one of the
best bio-insecticides in controlling CLW larvae infestations in
cotton fields.