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

Abstract

AbstractLarvae of Spilosoma obliqua Walker (Lepidoptera: Arctiidae) feed on leaves and flowers of green gram (or mung bean), Vigna radiata (L.) R. Wilczek (Fabaceae), and thereby reduce yield in India. Previously, we demonstrated that leaf surface waxes from three green gram cultivars – PDM 54 (PDM), Pusa Baisakhi (PUSA), and Samrat (SAM) – served as short‐range attractants and oviposition stimulants in S. obliqua. In this study, we aimed to find out whether flower surface waxes have similar roles. We identified the alkanes and free fatty acids in flower surface wax of the three cultivars, created representative blends of synthetic compounds, and tested the effects of crude wax and various blends on attraction and oviposition of S. obliqua. Twenty‐two n‐alkanes (n‐C13 to n‐C36) were identified in PDM, and 23 in the other two cultivars; pentadecane was predominant. Fifteen free fatty acids (C12:0 to C22:0) were detected in the three cultivars; palmitoleic acid (in PDM and PUSA) and pentadecanoic acid (in SAM) were predominant. In Y‐tube olfactometer bioassays, females were attracted to 1 mg flower surface wax of the three cultivars, as well as to blends composed of 3–7 compounds representative of the three varieties (PDM: tricosane, pentacosane, heptacosane, nonacosane, palmitoleic acid, linolenic acid, and stearic acid; PUSA: heptacosane, nonacosane, and stearic acid; and SAM: heptacosane, linolenic acid, and stearic acid). In dual choice tests, the females did not distinguish between surface wax of a variety and its representative synthetic blend. Also, they did not distinguish between the three cultivars. Results of oviposition assays were similar: 1 mg flower surface wax, as well as synthetic blends, stimulated egg laying, but the numbers of eggs were similar in the presence of surface wax of a variety vs. its representative synthetic blend. Also, oviposition was not differentially affected by cultivar. Thus, as in leaves, flower surface waxes act as short‐range attractants and oviposition stimulants in S. obliqua. The blends are potentially of use to develop lures as part of integrated pest management strategies.