Effectiveness of silicon on immature stages of the fall armyworm [Spodoptera frugiperda (J. E. Smith)

Abstract

ObjectivesFall armyworm (Spodoptera frugiperda) is a polyphagous pest causing economic losses to various crops. Commonly, chemical pesticides are used to control this pest, but these pesticides have a lot of side effects. Therefore, alternate environment-friendly method are inevitable for the management of S. frugiperda. Silicon (Si) supplementation to crop plants develops induced resistance against pests. MethodsAs the crop damage is done by the larval stage of the Fall armyworm, a laboratory experiment was carried out to investigate the impact of Si on immature stages of S. frugiperda. Treatments consisted of silicon dioxide (SiO2) and potassium silicate (K2SiO3) with two methods of application (foliar spray and soil application). No Si was the control treatment. ResultsThe current results showed that all Si treatments significantly (p ≤ 0.05) affected the immature stages of S. frugiperda. The foliar spray of SiO2 caused the highest larval mortality (40.33 ± 3.45 %) compared to K2SiO3 (29.33 ± 3.26 %) and control (4.67 ± 1.03 %). The greatest effect of Si treatments was observed in the early stages of larvae as insect mortality was significantly higher in 1st (19.67 ± 2.33 %) and 2nd (12.67 ± 1.03 %) instar of larval growth. Similarly, a significantly higher larval mortality was recorded one day (10.67 ± 2.07 %) and two days (19.67 ± 2.33 %) after hatching. Among Si sources, larval mortality was affected more in SiO2 than K2SiO3 and control. Meanwhile, the larval mortality was significantly more affected in Si's foliar spray (26.67 ± 17.26 %) than soil application (22.89 ± 14.46 %). A similar effect was observed in larvae to pupa ratio (59.67 ± 3.45 %), adult fecundity (146.67 ± 18.36 eggs), and neonate emergence (37.83 ± 4.62 %). In the pupa to adult ratio and adult sex ratio, no significant impact of Si sources or application methods was observed. ConclusionsThe current study results showed a significantly negative impact of Si on immature stages of S. frugiperda. Hence, Si application may diminish S. frugiperda colonization and initial damage in maize because it can decrease the fecundity of S. frugiperda and significantly increase the mortality of newly emerging larvae.