Relative Toxicity Of Insecticides Research Articles

Relative toxicity of insecticides against safflower aphid under laboratory condition

Relative toxicity of insecticides against safflower aphid under laboratory condition

Relative Bioefficacy of Some Newer Insecticides against Cowpea Aphid, Aphis craccivora (Koch) (Homoptera: Aphididae)

Relative toxicity of insecticides viz., clothianidin, bifenthrin, imidacloprid, spinosad, thiacloprid, flubendiamide, flonicamid and dimethoate is reported against cowpea aphid, Aphis craccivora Koch. Clothianidin @100 g a.i ha−1 was the most effective in bringing down the population of aphid at 1, 3, 7 DAS, while at 10 DAS, dimethoate (450 g a.i. ha−1) recorded the lowest incidence of aphid population (4.49 number per plant) with highest per cent reduction (79.19). The highest mean yield of 13.08 q ha−1 was obtained from dimethoate 450 g a.i. ha−1 followed by imidacloprid 20 g a.i. ha−1 (12.25 q ha−1) as compared to the lowest in the untreated plots (9.17 q ha−1). The highest benefit was achieved in the plots treated with imidacloprid 20 g a.i. ha−1 with a benefit-cost ratio of 8.72: 1 whereas the lowest benefit cost ratio of 0.37: 1 was obtained from the plots treated with spinosad 45 g a.i. ha−1. In laboratory, following dry film bioassay, the LC50 (at 24 h) of clothianidin, bifenthrin, imidacloprid, spinosad, thiacloprid, flubendiamide, flonicamid and dimethaote were found to be 0.031, 0.117, 0.063, 0.912, 0.042, 0.027, 0.079 and 0.057 ppm with the order of toxicity flubendiamide> clothianidin > thiacloprid > dimethoate >imidacloprid >flonicamid> bifenthrin >spinosad, respectively. Taking dimethoate as unity, the order of relative toxicity of insecticides was: flubendiamide (2.11)> clothianidin (1.83)> thiacloprid (1.35) > imidacloprid (0.90)>flonicamid (0.72)> bifenthrin (0.48)>spinosad (0.06) at 24 h. It was concluded that though dimethoate 450 g ai. ha−1 was an equally effective insecticide against A. craccivora as imidacloprid, the latter was more effective in terms of aphid population reduction, yield and benefit-cost ratio. Considering the LC 50 values and relative toxicity against A. craccivora, flubendiamide 60 a.i ha−1 was the most toxic and spinosad 45 a.i ha−1 the least toxic among the tested chemicals.

Residual Toxicity of Certain Newer Pesticides on Eupelmus tachardiae: A Parasitoid of Lac Insect Kerria lacca (Kerr)

The work addresses the issue of large scale lac crop mortality caused by parasitoids associated with lac insect, Kerria lacca (Kerr) in some of the lac growing tracts of the country. Laboratory evaluation of four selective insecticides viz., fipronil, indoxacarb, spinosad and ethofenprox was carried out at different concentrations against adults of a primary parasitoid of lac insect, Eupelmus tachardiae (Howard) by exposing the test insects on residual film of insecticides. Insecticides identified and their concentrations selected on the basis of their safety evaluation trials towards lac insect, K. lacca (Kerr). All these insecticides have been recommended and are being used on lac culture for the effective management of insect predators (Lepidopteran and Neuropteran) attacking lac insect. The recommended concentrations for effective management of lac insect predators are fipronil (0.007 %), indoxacarb (0.007 %), spinosad (0.005 %) and ethofenprox (0.02 %). Insecticide fipronil (varied from 0.0012 to 0.01 %), indoxacarb (varied from 0.0017 to 0.02 %) and ethofenprox (varied from 0.01 to 0.04 %) were evaluated at five different concentrations whereas spinosad was evaluated at eight concentrations (varied from 0.00015 to 0.01 %) against E. tachardiae. On the basis of relative residual toxicity, fipronil was found to be most effective treatment followed by spinosad and indoxacarb. Ethofenprox was found to be relatively least effective treatment against the test insect. Fipronil, indoxacarb and spinosad causes cent % mortality of male and female E. tachardiae adults within 24 h of exposure on residual film of insecticides whereas some adults survival was observed with the treatment of ethofenprox during the same exposure period. Cent % mortality of male and female test insect was recorded with the treatment of fipronil (0.007 %) within 1.5 h exposure whereas spinosad (0.005 %) was resulted to 88.5 and 82.4 % male and female mortality of test insect, respectively under same exposure period (1.5 h). However, exposure of test insect on residual film of indoxacarb (0.007 %) and ethofenprox (0.02 %) exhibited no mortality of test insect within 1.5 h exposure. Indoxacarb (0.007 %) caused 65.5 and 53.8 % male and female mortality, respectively whereas ethofenprox (0.02 %) caused mortality of male and female insect to the tune of 12.5 and 15.4 %, respectively within 6 h of exposure. The relative toxicity of insecticides based on time period of knockdown after exposure to residual film of insecticides may be depicted as fipronil > spinosad > indoxacarb > ethofenprox.

Ecological life table and relative toxicity of insecticides against leaf eating caterpillar,Spodoptera lituraFab. on groundnut

The life table and key mortality factors of Spodoptera litura Fabricius revealed that the mortality in the younger group larvae was 1.56 per cent due to bacterial infection and unknown reasons. Mortality in the older group larvae was 19.8 per cent due to diseases like NPV, N. rileyi, B. bassiana and parasites like Cotesia spp., and Tachinid maggot. Mortality in the pupal and adult stage was 7.98 & 2.15 per cent due to NPV and unknown reasons, respectively. Generation survival (SG) was worked out and it was 0.70. Value of trend index (I) was calculated to the tune of 0.018. Comparative relative toxicity of some modern insecticides against S. litura revealed that Emamectin benzoate was the most toxic and effective insecticide as its LC50 value was 0.000954, however, Spinosad was found to be the least toxic in which the LC50 value was worked out to the tune of 0.0158 in comparision to Chlorpyriphos, Flubendiamide, Rynaxypyr and Novaluron.

Relative toxicity of insecticides against diamondback moth (Plutella xylostellaL.) in cabbage (Brassica oleraceavar.capitata)

An experiment was conducted to evaluate the relative toxicity of some insecticides against 3rd instar larvae of diamondback moth, Plutella xylostella L. on cabbage (Brassica oleracea var. capitata) during 2007–08 and 2008–09. The order of relative toxicity of insecticides on the basis of LC50 values were spinosad > B.t.k. > cartap-hydrochloride > cypermethrin > quinalphos > endosulfan > azadirachtin. Spinosad had maximum relative toxicity (113.95) with lower LC50 values, 0.00038; whereas azadirachtin had lower relative toxicity (0.014) with higher LC50 values, 3.1565.

Toxicity of insecticides to the citrus leafminer, Phyllocnistis citrella, and its parasitoids, Chrysocharis pentheus and Sympiesis striatipes (Hymenoptera: Eulophidae)

The experiments were conducted to learn about the relative toxicity of insecticides against the two parasite wasps of citrus leafminer (CLM), Phyllocnistis citrella. The relative toxicity of 12 common insecticides against the eggs and first instar larvae of the pest, and its parasitoids of Chrysocharis pentheus and Sympiesis striatipes, which are dominant species in Ehime Prefecture, was compared in 2003. Corrected mortalities were evaluated by dipping or spraying methods for the CLM eggs and larvae, and by clip-cage bioassay for the parasitoid wasps. All the insecticides tested showed almost over 90% mortality to the first instar larvae of citrus leafminer, but a lesser effect to the eggs. Against the adult parasitoids, imidacloprid (a.i. 0.005%), thiamethoxam (a.i. 0.003%) and acetamiprid (a.i. 0.005%) of the nicotinoide insecticides were less toxic, but dinotefuran (a.i. 0.02%) showed rather high mortalities. Of the IGRs, teflubenzuron (a.i. 0.05%) and diflubenzuron (a.i. 0.012%) were safe or less toxic to adult wasps. These three nicotinoide and two IGRs insecticides will be suitable candidates for use in the IPM program. Isoxathion (a.i. 0.025%) and primiphose-methyl (a.i. 0.056%) of the organophosphate and alanycarb (a.i. 0.04%) of carbamate were highly toxic. Bifenthrin (a.i. 0.0015%) of the pyrethroid and petroleum oil (a.i. 1.05%) were moderate in toxicity. Clothianidin (a.i. 0.005%) of the nicotinoide showed low toxicity to Chrysocharis pentheus but moderate toxicity to Sympiesis striatipes.