The importance of leaf surface wax compounds from the rice-field weed Ludwigia octovalvis (Jacq.) Raven (Onagraceae) was determined in the flea beetle Altica cyanea (Weber) (Coleoptera: Chrysomelidae). Extraction, thin layer chromatography and GC-MS and GC-FID analyses of surface waxes of young, mature and senescent leaves revealed 20, 19 and 19 n-alkanes between n-C15 and n-C35, respectively; whereas 14, 14 and 12 free fatty acids between C12:0 and C22:0 fatty acids were identified in young, mature and senescent leaves, respectively. Tricosane was predominant n-alkane in young and mature leaves, whilst eicosane predominated in senescent leaves. Heneicosanoic acid, palmitic acid and docosanoic acid were the most abundant free fatty acids in young, mature and senescent leaves, respectively. A. cyanea females showed attraction to 0.25 mature leaf equivalent surface waxes compared with young or senescent leaves in a short glass Y-tube olfactometer bioassay. The insects were attracted to a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml−1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively, comparable with the proportions as present in 0.25 mature leaf equivalent surface waxes. A. cyanea also laid eggs on a filter paper moistened with 0.25 mature leaf equivalent surface waxes or a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml−1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively. This finding could provide a basis for monitoring of the potential biocontrol agent in the field.

Larvae and adults of Altica cyanea (Weber) (Coleoptera: Chrysomelidae) feed on the rice-field weed Ludwigia octovalvis (Jacq.) Raven (Onagraceae), commonly known as willow primrose, which is considered a biocontrol agent of the weed. Volatile organic compounds from undamaged plants, plants after 4, 12, and 36 h of continuous feeding by A. cyanea larvae or adult females and after mechanical damaging were identified by GC-MS and GC-FID analyses. Twenty nine compounds were identified from undamaged plants. 2Z-Penten-1-ol, geraniol, and 1-tridecanol were present in all plants damaged by larvae. In contrast, feeding by adults caused the release of 2Z-penten-1-ol only after 12 and 36 h; whereas geraniol and 1-tridecanol appeared only after 36 h. Farnesyl acetone was detected after 12 and 36 h of feeding by larvae and after 36 h of feeding by adults. Farnesene was detected after 36 h of feeding by larvae and adults. Linalool was unique after 36 h of feeding by larvae. In Y-shaped glass tube olfactometer bioassays, A. cyanea females were attracted to volatiles after 36 h of feeding by larvae or adults compared to volatiles released by undamaged plants. The insects were attracted to five synthetic compounds: 3-hexanol, α-pinene, linalool oxide, geraniol, and phytol. Synthetic blends were more attractive than individual compounds. Compared to undamaged plants, volatiles released by plants, damaged by conspecific individuals, were more attractive to A. cyanea females, due to elevated emissions of 3-hexanol, α-pinene, linalool oxide, geraniol, and phytol.

Ludwigia adscendens (L.) Hara, Ludwigia parviflora Roxb., and Ludwigia octovalvis (Jacq.) Raven (Onagraceae) are abundant weeds in rice fields in India. These weeds compete with rice for resources in fields and this results in reduction of grain yield. Altica cyanea (Weber) (Coleoptera: Chrysomelidae) is a biocontrol agent of the three rice-field weeds. Hence, it is relevant to study host preference of A. cyanea using volatile cues of these three weeds. Therefore, we attempted to identify volatiles from leaves of the three Ludwigia species attracting A. cyanea, which could be used as an attractant during early emergence of the weeds in rice fields. In Y-tube olfactometer assays, A. cyanea females were more attracted to natural volatiles of plants after 48 h of feeding by adults than to volatiles of undamaged plants. The volatile organic compounds from undamaged plants, and plants after 6 and 48 h of feeding by A. cyanea were identified and quantified by gas chromatography and mass spectrometry (GC-MS) and GC-flame ionization detection (FID), respectively. In total, 25, 29, and 29 volatile compounds were detected in headspaces of undamaged L. adscendens, L. parviflora, and L. octovalvis, respectively, whereas 32, 35, and 34 compounds, respectively, were detected after 48 h of feeding by A. cyanea. Methyl jasmonate predominated among the volatile compounds in all treatments, but this compound was not attractive to A. cyanea. Females were attracted by synthetic blends of 3-hexanol, a-pinene, linalool oxide, and phytol in amounts mimicking those in each of the three Ludwigia species after 48 h of feeding by A. cyanea. The blends mimicking L. adscendens and L. parviflora included geraniol, whereas the blend mimicking L. parviflora also included 1-tridecanol. These synthetic blends may be helpful to monitor A. cyanea in biocontrol programmes.

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.

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