Repellence or attraction: secondary metabolites in pepper mediate attraction and defense against Spodoptera litura

Resistance to insect pests is an important self-defense characteristic of pepper plants. However, the resistance of different pepper cultivars to Spodoptera litura larvae, one of the main insect pest species on pepper, is not well understood.

Among seven pepper cultivars evaluated, cayenne pepper 'FXBX' showed the highest repellency to third instar S. litura larvae, Chao tian chili pepper 'BLTY2' showed the lowest repellency. Plant volatiles (1-hexene, hexanal, β-ionone, (E,E)-2,6-nonadienal, and methyl salicylate) affected host selection by S. litura. Among these, 1-hexene, hexanal, and β-ionone at concentrations naturally-released by pepper leaves were found to repel S. litura. Interestingly, S. litura larvae fed on the larva-attracting pepper cultivar, (BLTY2) had an extended developmental period, which was about 13 days longer than larvae fed on FXBX. Besides, the survival rate of larvae fed on BLTY2 was 22.5 ± 0.0%, indicating that the leaves of BLTY2 can kill S. litura larvae. Correlation analysis showed that larval survival rate, emergence rate, female adult longevity, and pupal weight were positively correlated with the vitamin C, amino acids, protein, cellulose, and soluble sugar contents, but were negatively correlated with wax and flavonoids contents.

We identified two different modes of direct defense exhibited by pepper cultivars against S. litura. One involves the release of repellent volatiles to avoid been fed on (FXBX cultivar). The other involves the inhibition of the growth and development or the direct killing of S. litura larvae which feeds on it (BLTY2 cultivar). © 2022 Society of Chemical Industry.