Lethal, sub-lethal and persistent toxicity of spinosyn and diamide insecticides against Spodoptera litura (Fab.) and Spilarctia obliqua (Wlk.)
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Date
2019-06
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
A detailed investigation was undertaken to determine the bioefficacy of spinosyn and diamide insecticides against Spodoptera litura (Fabricius) and Spilarctia obliqua (Walker); effect of sublethal concentrations on growth and development parameters of S. litura; effect on feeding behaviour of S. litura and S. obliqua and persistent toxicity on cowpea (Vigna unguiculata L. Walp.) and soybean (Glycine max L.) against S. litura. All the experiments were conducted in Insecticide Toxicology Laboratory of the Department of Entomology. The stomach and contact toxicity of spinosyn (spinetoram and spinosad) and diamide (chlorantraniliprole and flubendiamide) insecticides was tested against 4d old larvae of S. litura by leaf smear and larval atomization methods on castor leaf disc under laboratory conditions. The LC50 values of spinetoram were 0.0121, 0.0085, 0.0034 and 0.0018% at 24, 36, 48 and 72 hours after exposure (HAE), respectively in case of larval atomization method; and were 0.0047 and 0.0032% at 24 and 36 hours after feeding (HAF), respectively in leaf smear method, showing 2.57 and 2.66 times more stomach toxicity than contact toxicity at 24 and 36 HAF/HAE, respectively. The LT50 values of spinetoram at 0.01, 0.005 and 0.002% concentrations were 33.91, 37.76 and 51.78h, respectively in larval atomization method; at 0.005% concentration was 27.54h by leaf smear method. The LC50 values of spinosad were 0.0225, 0.02 and 0.0185% at 36, 48 and 72 HAE, respectively by larval atomization method and; 0.0316, 0.0182 and 0.0110% at 24, 36 and 48 HAF, respectively by leaf smear method. The stomach toxicity of spinosad (LC50= 0.0182 and 0.0110%) was 1.24 and 1.82 times more than the contact toxicity (0.0225 and 0.02%) at 36 and 48 HAF/HAE, respectively. The LT50 values of spinosad at 0.05 and 0.04% concentrations were 23.8 and 30.83h, respectively in larval atomization method; at 0.04, 0.03, 0.02 and 0.01% concentration were 21.11, 28.06, 35.45 and 49.70h, respectively in leaf smear method. The LC50 values of chlorantraniliprole were 0.00112 and 0.00086%, respectively at 36 and 48 HAE by larval atomization method, however were 0.0042 and 0.0009%, respectively at 24 and 36 HAF by leaf smear method, showing 1.24 times higher stomach toxicity than contact toxicity at 36 HAF/HAE. The LT50 values at 0.005 and 0.002% concentration of chlorantraniliprole were 25.05 and 25.18h, respectively in larval atomization method. In leaf smear method at 0.001 and 0.0001% concentration of chlorantraniliprole, the LT50 values were 28.03 and 53.22h, respectively. The contact toxicity of flubendiamide in terms of LC50 values were 0.005 and 0.0038%, respectively at 48 and 72 HAE by larval atomization method. The effect of sublethal concentrations of spinetoram and flubendiamide on growth and development parameters was tested against 5d old larvae of S. litura by leaf smear method on soybean leaf disc. At 3 days after feeding (DAF), flubendiamide (0.009%) and spinetoram (0.01%) reduced the mean weight gain over control by 110.7 and 62.97% and caused 66.6 and 40% mortality, respectively. Pupation was zero at flubendiamide (0.009%) whereas in spinetoram (0.01%) it was 53.34%. In another experiment the effect of sublethal concentration of spinosad was evaluated against 4d old larvae of S. litura by larval atomization method. At 4 days after treatment (DAT), spinosad (0.005%) caused 37.24% reduction in weight gain over control. The feeding inhibitory activity of flubendiamide, spinetoram and spinosad were determined against 6d old larvae of S. litura by leaf smear method on castor leaf disc. The order of deterrence against S. litura was flubendiamide > spinetoram > spinosad at the higher concentration (0.01%) and at lower concentration (0.002, 0.0002 and 0.00005%) the order was flubendiamide > spinosad > spinetoram.
The persistent toxicity of three insecticides viz. flubendiamide, chlorantraniliprole and spinetoram has been determined on cowpea and soybean against 4d old larvae of S. litura. On cowpea spinetoram @ 0.01% was the most persistent insecticide with a PT value of 759.96 followed by flubendiamide @ 0.01% (597.24) and chlorantraniliprole @ 0.006% (575.00) at 24 HAF. After 72 hours of feeding on the treated leaves, spinetoram again showed highest PT value of 1897.2 followed by chlorantraniliprole (1542.72) and flubendiamide (1279.98). On soybean spinetoram @ 0.01% was the most persistent insecticide with a PT value of 740.16 followed by chlorantraniliprole @ 0.006% (PT= 491.60) and flubendiamide (476.00) at 24 HAF. At 72 HAF, spinetoram showed highest PT value of 1954.32 followed by chlorantraniliprole (1554.24) and flubendiamide (1485.60). The contact toxicity of flubendiamide and spinetoram against 10d old larvae of S. obliqua by larval atomization method showed that the LC30, LC50 and LC90 value of flubendiamide at 36 HAE were 0.00015, 0.00072 and 0.035%, respectively and at 48 HAE the values were 0.00014, 0.00068 and 0.0306%, respectively. In case of spinetoram, at 24 HAE therefore LC at 36 and 48 HAE could not be recorded. The LC30, LC50 and LC90 values of spinetoram at 12 HAE were 0.000086, 0.00031 and 0.0072%, respectively, and at 24 HAE were 0.000037, 0.00013 and 0.0034%, respectively. The LT value at 0.01% concentration of flubendiamide against 14d old larvae of S. obliqua was 18.61h (LT30), 27.95h (LT50) and 76.01h (LT90) by larval atomization method. The feeding inhibitory activity of flubendiamide, spinetoram and spinosad were determined against 12d old larvae of S. obliqua by leaf smear method on castor leaf disc. The order of deterrence against S. obliqua was flubendiamide > spinetoram > spinosad at the higher concentration (0.01%) and at lower concentration (0.002, 0.0002 and 0.00005%) the order was flubendiamide > spinosad > spinetoram.
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