The importance of leaf surface wax as short‐range attractant and oviposition stimulant in a generalist Lepidoptera

Abstract

Green gram, Vigna radiata (L.) Wilczek, is an important pulse crop of Asia. Severe attack by the larvae of Spilosoma obliqua Walker (Lepidoptera: Arctiidae) causes defoliation of green gram and reduces seed yield. Females lay eggs on the leaf surface, and therefore, surface wax plays an important role as short‐range attractant and oviposition stimulant. So, we have attempted to find out whether leaf surface wax compounds (alkanes and free fatty acids) from three green gram cultivars (PDM 54, PUSA BAISAKHI and SAMRAT) could act as short‐range attractant and oviposition stimulant in females. The TLC, GC‐MS and GC‐FID analyses of n‐hexane extracts revealed 20 n‐alkanes from n‐C15 to n‐C36 and 13 free fatty acids from C12:0 to C21:0, whilst linoleic acid was unique in SAMRAT. Pentacosane was the predominant amongst n‐alkanes in the leaf surface waxes of three cultivars. Heneicosanoic acid and palmitoleic acid were the predominant free fatty acids in the leaf surface waxes of PDM 54, and PUSA BAISAKHI and SAMRAT, respectively. Females were attracted towards one leaf equivalent surface wax of three green gram cultivars against solvent controls (n‐hexane) in Y‐tube olfactometer bioassays. A synthetic blend of pentacosane, heptacosane, nonacosane, hexatriacontane, palmitoleic acid, linolenic acid and stearic acid, a synthetic blend of pentacosane, hexatriacontane and stearic acid, and a synthetic blend of hexatriacontane, linolenic acid and stearic acid resembling in amounts present in one leaf equivalent surface wax of PDM 54, PUSA BAISAKHI and SAMRAT, respectively, served as short‐range attractant and oviposition stimulant in females. Females showed equal preference for egg laying towards the above three synthetic blends when these blends were tested against each other, and hence, these blends could be employed in development of baited traps in pest management strategies.

Flower surface wax chemicals in green gram help to stimulate oviposition in Spilosoma obliqua within short distances

“…Furthermore, flower surface waxes of two Lathyrus sativus L. cultivars, as well as representative synthetic blends consisting of various n-alkanes and fatty acids, attracted and stimulated oviposition of the aphid Aphis craccivora Koch (Mitra et al, 2020a). In an earlier study, we demonstrated that natural leaf surface waxes, as well as synthetic blends of alkanes and fatty acids resembling leaf surface wax chemicals, of three green gram cultivars (PDM 54, Pusa Baisakhi, and Samrat) served as short-range attractants and oviposition stimulants in S. obliqua females (Mobarak et al, 2020b). However, the role of green gram flower surface waxes has not been explored.…”

“…The single hydrocarbon band on each TLC plate was eluted from the silica gel layer with 25 ml chloroform. Alkanes in each sample (n = 5) were identified using gas chromatography-mass spectrometry (GC-MS) and quantified using GC-flame ionization detection (GC-FID) following the protocol of Mobarak et al (2020b) (Supporting Information S1).…”

“…The aqueous layer was discarded and the hexane fraction was passed through 50 g anhydrous Na 2 SO 4 twice. Free fatty acids in each sample (n = 5) were identified using GC-MS and quantified using GC-FID following Mobarak et al (2020b) (Supporting Information S2).…”

“…An insect herbivore often recognizes a host plant from a long distance by the volatile organic compounds (VOCs) it emits. Surface waxes from leaves and flowers, with limited volatility, provide short-range attractants and oviposition stimulants (Müller & Hilker, 2001;Schoonhoven et al, 2005;Das et al, 2019;Fernández et al, 2019;Mitra et al, 2020a,b;Mobarak et al, 2020b). Hence, elucidation of leaf and flower surface wax chemicals that affect insects of economic importance is vital, due to their potential for use in the manipulation of insect behavior in crop fields; they could be used to develop baits for traps as part of an integrated pest management (IPM) strategy, which could help to reduce the harmful effect of synthetic insecticides on ecosystem health.…”

Behavioral Responses of a Generalist Pest, Spilosoma Obliqua Walker, Towards the Leaf Surface Wax Chemicals of Three Types of Jute Crop and Implications in Pest Management

“…Precise knowledge about chemical mediated plant-insect interactions between the bre crops and the pest, S. obliqua, is required for their successful IPM. For many years, numerous studies have been conducted to control insect pests through plant-based semiochemicals (Mobarak et al 2020a; Roy 2019a 2021b). Isolation and identi cation of semiochemical compounds responsible for triggering insect behaviour can enhance a better understanding of insect-plant interactions (Little et To apply the chemical ecological approach, S. obliqua females, as well as their 5 th instar larvae, were tested in a series of bioassays for attraction, oviposition, and feeding preferences on the three potential host (three jute cultivars) plants in the present study.…”