Browsing by Author "Binseena,S R"

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Nucleopolyhedrovirus mediated biointensive management of polyphagous pest Spodoptera litura F.
(Department of Agricultural Entomology,College of Agriculture,Vellayani, 2025-09-12) Binseena,S R; Faizal,M H
The study entitled ‘Nucleopolyhedrovirus mediated biointensive management of polyphagous pest Spodoptera litura F. was carried out at the Department of Entomology, College of Agriculture, Vellayani, during 2019-2024 with the objective of development and evaluation of liquid and bait formulations of Spodoptera litura nucleopolyhedrovirus (SlNPV) incorporating botanicals and identification of viral gene sequences (iap and egt) of pesticidal relevance in SlNPV genome. Bioassay of botanical oils such as neem, pongam, and cashew nut shell liquid (CNSL) was done against S. litura under laboratory conditions. Cent percentage mortality of larvae was observed for neem oil 4 % and pongam oil 10 % treatments at 144 HAT and CNSL 5 % at 168 HAT. The LT50 values of the botanical oils were computed to 142.45, 146.37, and 176.54 hours for neem oil 4 %, pongam oil 10 %, and CNSL 3 % respectively with corresponding LT90 values of 329.04, 625.90, and 357.84 hours. In the bioassay of SlNPV, 100 % mortality was caused by the treatments with 1010 and 109 POB mL-1 which was at par with the mortality caused by lower concentrations of 108 and 107 POB mL-1 at 192 HAT. The effective doses (ED) of neem oil, pongam oil and CNSL were arrived at as 3.4 %, 4 %, and 2.5 % respectively by critically assessing the three important parameters of mortality, LC50 value and leaf area damage. A combination treatment of SlNPV (107 POB mL-1) and different doses (ED, ¾ ED, ½ ED, and ¼ ED) of botanical oils was attempted with the aim of reducing the lethal time of SlNPV. Significantly high mortality of S. litura (53.33 %) could be achieved in the combination treatments of SlNPV + neem oil 2.5 % as early as 48 HAT. However, at 144 HAT both SlNPV + neem oil 2.5 % and SlNPV + pongam oil 3 % treatments could result in 93.33 % mortality as against 60 % for treatment with SlNPV alone. The development of emulsifiable suspension (ES) formulations of SlNPV was attempted employing different oils as base. Isopropanol was identified as the solvent since it could solubilize all the oils tried at 5 % concentration, with low turbidity and viscosity. Emulsifier combinations of Span 20 + Triton X -100 (29:71) at 5 % for neem oil, sunflower oil, coconut oil, mustard oil, as well as Span 20 + Tween 80 (47:53) at 12 % for pongam oil, all yielding HLB value of 12 produced excellent bloom of Score 5 upon emulsification. SlNPV was dispensed into the oil-solvent-emulsifier combination so as to yield a final concentration of 1010 POBs mL-1. Among the five ES formulations evaluated, neem oil based (ES1) and pongam oil based (ES2) formulations were found to be superior producing significantly high mortality of 100 % and 93.33 % respectively even after 7 months of storage. Boric acid 1 % was selected and added to the formulation since it yielded superior protection of SlNPV with OAR (original activity remaining) value of 65.72 % upon exposure to sunlight. Development of storable ready to use bait formulations containing SlNPV and botanical oils were attempted, utilizing selected combination base matrices containing any two of wheat bran (WB), wheat flour (WF), rice bran (RB), and chickpea flour (CF) along with additives (A) (jaggery, cornstarch, CMC) as well as artificial diet alone. Based on the feeding preference and bait consumption by S. litura in free-choice and no-choice situations respectively three base matrices viz., artificial diet, WF (75 %) + CF (25 %) and WB (65 %) + WF (35 %) + A were selected, into which SlNPV (107 POB g-1) and either neem oil (2.5 %) or pongam oil (3 %) were infused. All three baits thus developed exhibited satisfactory structural integrity upon dehydration and rehydration. WB + WF based two bait formulations B3 and B2 of SlNPV containing pongam oil and neem oil respectively, were found to produce significantly high mortality of S. litura (100 % and 93.33 % respectively). Superior emulsifiable suspension and bait formulations alone and in combinations of the ones having the same botanical oil were evaluated for the management of S. litura in okra under polyhouse conditions. Combined application of an emulsion of ES2 and bait formulation B3 containing both SlNPV and pongam oil produced 96.67 % mortality of S. litura at 7 DAT, an effect on par with the chemical insecticide Flubendiamide 39.35 % SC. Identification of viral genes iap and egt, of pesticidal relevance was attempted in SlNPV for which specific primers with oligonucleotide sequences forward 5' GATTCGATCGCTGTCAACCT-3' reverse 5'-TTTCACTTTGGATGCTGCCT-3' and forward 5'-ATGGACTCGAACATGTTGGAC-3' reverse 5' AAGTCGAACATTGCGTATTTGG-3' respectively were constructed. Amplicons of size 500 bp and 600 bp could be detected in PCR with these primers, indicating the presence of both iap and egt sequences in SlNPV. The combined application of emulsifiable formulation ES2 [containing SlNPV (1010 POB mL-1), pongam oil (82 %), isopropyl alcohol (5 %), Span 20 + Tween 80 in the ratio 47:53 (12 %) and boric acid (1 %)] and bait formulation B3 [containing SlNPV (107 POB g-1 ), pongam oil (3 %), base matrix of WB + WF in the ratio 65:35 (77 %), jaggery (19 %), corn starch (0.3 %) and CMC (0.7 %)], developed in the present study each delivering SlNPV and pongam oil @ 107 POB mL-1/g-1 and 3 % respectively upon application was found effective in managing S. litura and have the potential to be developed as the predominant eco-friendly tactic in its IPM.