Bioefficacy, persistent toxicity and sublethal effects of certain insecticides and mixed formulations against polyphagous insect pests
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Date
2019-09
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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 some insecticides and mixed formulations against Dysdercus cingulatus (Fabricius), Spodoptera litura (Fabricius), Spilarctia obliqua (Walker) and Henosepilachna vigintioctopunctata (Fabricius); persistent toxicity on mulberry, rajma and moong bean against S. litura; effect on feeding behaviour of S. litura and S. obliqua; influence of host plants on susceptibility of S. litura to some insecticide and effect of sublethal concentrations on growth and development parameters of S.litura and S. obliqua. All the experiments were conducted in Insecticide Toxicology Laboratory of the Department of Entomology. Quinalphos (LC50= 0.00041 %) showed better contact action against 3rd instar nymphs of D. cingulatus compared to chlorpyriphos (0.00092 %) by residue contact bioassay method at 72 HAE; and among five synthetic pyrethroids, bifenthrin (0.0004 %) showed better contact action followed by cypermethrin (0.00052 %) at 72 HAE, whereas alphamethrin resulted in an LC50 of 0.0002 % at 96 HAE against 4th instar nymph. Spinetoram + methoxyfenozide (LC50= 0.0016 %, 48 HAF) was found effective against 5 d old larvae of S. litura at lethal and sublethal concentrations showing a good stomach toxicity and significantly affected the growth and development of S. litura by leaf dip method. Among two combinations, cypermethrin + indoxacarb (0.0028 %) was found more effective than flubendiamide + thiacloprid (0.0203%) against 6 d old larvae of S. litura by leaf smear method on soybean. On castor, chlorantraniliprole + lambda-cyhalothrin (Lc50= 0.0009%. 96 HAF) showed better stomach toxicity and inhibited feeding by 97.16 %, followed by cypermethrin + indoxacarb (0.0035%, 72 HAF) and spinetoram (0.0093%, 72 HAF); however by residue contact bioassay method, cypermethrin + indoxacarb (0.0040 %, 24 HAE) showed a faster contact action followed by spinetoram (0.0049%, 48 HAE) and chlorantraniliprole + lambda-cyhalothrin (0.0066%, 72 HAE) against 5 d old larvae of S. litura. Among IGRs, lufenuron was most effective in reducing the feeding (23.16 % feeding inhibition, at 0.0005 %, 48 HAF) of 3 d old larvae of S. litura and by leaf smear method and resulted in LC50 value of 0.00018 % (72 HAF); lufenuron @ 0.00007 %, buprofezin 0.05 % pyriproxyfen 0.05% and buprofezin + fipronil @ 0.1 % resulted in increased larval and pupal duration, reduction in larval and pupal weight, lower pupation and reduced emergence of adults. Spinetoram + methoxyfenozide (LC50= 0.0004%, 60 HAF) was most effective combination insecticide against 4 d old larvae of S. litura by leaf smear method followed by cyantraniliprole + lufenuron (0.0037 %) and indoxacarb + acetamiprid (0.0063%); whereas, by larval atomization method, indoxacarb + acetamiprid (LC50= 0.0030%, 36 HAE) showed better contact action compared to cyantraniliprole + lufenuron (0.0092 and 0.0029 %, at 36 and 48 HAE) and spinetoram + methoxyfenozide (0.0031 %, 48 HAE). Rajmah bean as a host plant was most effective in terms of increasing the susceptibility of larvae owing to the reduced weight gain and higher mortality of larvae in different insecticides compared to mulberry and castor plants. Chlorantraniliprole + lambda cyhalothrin 3.61 and 4.10 times lesser time duration was required in rajmah to cause 50% mortality compared to mulberry and castor. Chlorantraniliprole + lambda-cyhalothrin at sublethal concentration was most effective against 5 d old larvae of S. litura producing profound effect on growth (96.26 and 70.81 % reduction in weight gain over control, 0.0001 % at 3 and 6 DAF) and feeding (75.07 % feeding inhibition, at 0.0001%,48 HAF) respectively; spinetoram + methoxyfenozide showed least effect, however the concentration used was also almost 10 or more times lower compared to flubendiamide + thiacloprid and cypermethrin + indoxacarb. The persistent toxicity of different insecticides was tested on mulberry, rajmah and mung bean plants. Chlorantraniliprole + lambda-cyhalothrin @ 0.027 % showed highest persistence (PT value= 1841.60, 24 HAF), followed by cypermethrin + indoxacarb @ 0.02% (812.68) and beta-cyfluthrin + imidacloprid @ 0.012% (216.65) on mulberry; and the order of persistent toxicity on rajmah plant was chlorantraniliprole + lambda-cyhalothrin (0.027%) > chlorantraniliprole + lambda-cyhalothrin (0.014%) > cypermethrin + indoxacarb (0.02%) > chlorantraniliprole + lambda-cyhalothrin (0.007%) > emamectin benzoate (0.0019%) > betacyfluthrin + imidacloprid (0.012 %.) against 5 d old larvae of S. Litura. Chlorantraniliprole @ 0.0055% persisted for a longer duration on mung bean (15 DAS, 1072.50) compared to rajmah bean (11 DAS, 916.52) plant. In another experiment, buprofezin + fipronil @ 1.023% (PT value = 2879.68, 72 HAF) was most persistent combination insecticide on rajmah bean, however the dose applied was 100 to 1000 times higher than other tested insecticides. Thus lufenuron @ 0.004 % (PT value = 1979.91, 72 HAF) and spinetoram + methoxyfenozide @ 0.017% (2309.85) can be used as a better alternative, persisting for a fairly longer period of 27 days. Spinetoram + methoxyfenozide showed a better contact toxicity (LC50= 0.0016 %) compared to stomach (0.0022 %) action by larval and leaf atomization method against 13 d old larvae of S. obliqua, respectively. Chlorantraniliprole + lambda-cyhalothrin @ 0.0001 % was most effective combination causing a profound sublethal effects on growth and development of 6 d old larvae of S. Obliqua by leaf smear method and significantly reduced the feeding (97.11 % feeding inhibition at 0.01 % 48 HAF); spinetoram + methoxyfenozide was most effective in terms of mortality causing 70 % mortality within 72 HAF compared to no mortality in other combinations, at 0.0001%. Lufenuron (LC50= 0.00008 %, 48 HAE) and emamectin benzoate (0.00009 and 0.00006 %, at 48 and 72 HAE) gave almost equitoxic responses showing a higher contact toxicity compared to chlorantraniliprole (0.0005, at 72 HAE) against 9 d old larvae of S. obliqua by larval atomization method. Deltamethrin + triazophos, chlorpyriphos + cypermethrin and profenofos + cypermethrin (LC50= 0.0003, 0.0002 and 0.0003 %, 48 HAE) were more or less equally effective via contact action against 10 d old grubs of H. vigintioctopunctata. The order of toxicity of different combination insecticides was beta-cyfluthrin + imidacloprid (0.0003%) > chlorpyriphos + cypermethrin (0.0017%) > deltamethrin + triazophos (0.0045%) > profenofos + cypermethrin (0.021%) > ethion + cypermethrin (0.0256%) > cypermethrin + indoxacarb (0.056%), at 48 HAF, with chlorpyriphos + cypermethrin and cypermethrin + indoxacarb showing 5.66 and 186.66 times less toxicity than beta-cyfluthrin + imidacloprid against 4-5 d old adult of H. vigintioctopunctata, respectively.
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