Toxicity of spinetoram and combination insecticides and its effect on feeding of Spodoptera litura (F.)

Abstract

The stomach and contact toxicity of four insecticides was evaluated on 5 days old larvae of Spodoptera litura (F.) by leaf smear method on castor leaf disc and residue contact method on glass surface under laboratory conditions, respectively. Spinetoram (LC50= 0.0105 and 0.0049%) showed 2.14x better contact toxicity than stomach action, respectively at 48 hr after exposure (HAE)/hours after feeding (HAF). Cypermethrin+ indoxacarb (LC50= 0.0040 at 24 HAE and 0.0035% at 72 HAF) showed 1.55x and 2.66x higher contact and stomach toxicity than spinetoram (0.0062 and 0.0093%), respectively. Chlorantraniliprole+ lambda cyhalothrin (LC50= 0.0066 at 72 HAE and 0.0009% at 96 HAF) showed 4.54x and 26.22x better contact and stomach action than flubendiamide+ indoxacarb (0.0300 and 0.0236%, respectively). Also, chlorantraniliprole+ lambdacyhalothrin (mean leaf area consumed-MLAC = 0.28 cm2/larva) was the most effective in reducing the feeding showing 96.91% reduction in MLAC over control (9.05 cm2/larva), at 0.005% concentration, 48 HAF. In another experiment, the stomach toxicity of two combination insecticides was evaluated against 6 days old larvae of S. litura by leaf smear bioassay method on soybean leaves. At 48 HAF LC50 of cypermethrin+ indoxacarb (0.0028%) showed 7.09x higher stomach toxicity than flubendiamide+ thiacloprid (0.0203%).