Effect of Silicon and Plant Growth Regulators on the Biology and Fitness of Fall Armyworm, Spodoptera frugiperda, a Recently Invaded Pest of Maize in India

Silicon (Si) and Plant growth regulators (PGR's) are known to induce resistance against various insect pests. A study was conducted to determine the effect of Si and PGR's on biology and induced resistance in maize against recently invaded fall armyworm (FAW), Spodoptera frugiperda. Different foliar silicic acid (FSA), gibberellic acid (GA(3)) and jasmonic acid (JA) at different concentrations and combinations were evaluated. The larvae fed on plants treated with FSA, FSA + GA(3) and jasmonic acid exhibited lower larval, pre-pupal and pupal weight, whereas no effect of gibberellic acid alone on these parameters. Application of FSA at 2 ml L(-1)and GA(3) 0.5 mg plant(-1) significantly decreased the larval weight (18.38 mg at 5th day, 219.35 mg at 10th day), pre-pupal weight (168.64 mg), pupal weight (158.22 mg) and larval survival (70.00%), fecundity (500.20 eggs/female) and fertility (62.68%). Male longevity was decreased by all the treatments except with the application of GA(3) and JA and female longevity was unaffected by JA. The biological parameters of S. frugiperda were negatively correlated with increase in Si, phenols and tannins and potassium concentration in leaves. The study conclusively demonstrated significant negative effect on various biological parameters of FAW when plants were treated with Si and PGR's.