Synergism in Host Selection Behavior of Three Generalist Insects Towards Leaf Cuticular Wax of Sesame Cultivars.

Abstract

Leaf cuticular wax plays important role in host selection, oviposition, and feeding of phytophagous insects. Thus, the role of cuticular wax of sesame (Sesamum indicum) cultivars (Savitri and Nirmala) in host selection of 3 generalist pests (Spilosoma obliqua Walker, Helicoverpa armigera Hübner, and Spodoptera litura Fabricius) was investigated under laboratory conditions. The GC-MS and GC-FID analyses of leaf surface waxes of both cultivars indicated the presence of 14 n-alkanes from n-C9 to n-C44 and 12 free fatty acids (FFAs) from C9:0 to C20:0. The most predominant n-alkane and FFA of the cultivars were n-C26 (94.3 ± 7.27 μg leaf-1) and C18:1 (110.8 ± 10.07 μg leaf-1), respectively present in Savitri cultivar. The generalists used visual (color and shape), olfactory (odorous n-alkanes and FFAs), tactile (surface ultra-structure), and gustatory (cuticular wax) cues in a synergistic manner for their host selection through attraction (adults and larvae) followed by oviposition (adults) and feeding (larvae) on studied cultivars (Savitri > Nirmala). Their olfactory responses were maximum towards 2 leaf equivalent amount, whereas oviposition and feeding preference were maximum towards 4 leaf equivalent amount of the combined synthetic (4 n-alkanes (n-C16, n-C22, n-C24, n-C26) + 3 FFAs (C12:0, C14:0, C18:1)) mixture-treated intact leaf of cultivar Savitri. This finding can suggest that the synthetic blend (4 n-alkanes + 3 FFAs) in leaf equivalent amount (396.6 ± 4.13 μg leaf-1) or more from cultivar Savitri can be used as lures to develop baited trap. In addition, the cultivar Nirmala can be used as a resistant cultivar in the ecological pest management (EPM) framework of these target pest species.