SPECIAL ISSUE: INSECTS IN AGROECOSYSTEMS Attraction of the potential biocontrol agent Altica cyanea by volatile compounds of three species of Ludwigia weeds from rice fields Saubhik Mitra, Amarnath Karmakar, Swati Das & Anandamay Barik Ecology Research Laboratory, Department of Zoology, The University of Burdwan, Burdwan, West Bengal, 713 104, India Accepted: 17 August 2019 Key words: Ludwigia adscendens, Ludwigia parviflora, Ludwigia octovalvis, Onagraceae, monitoring, Altica cyanea, Coleoptera, Chrysomelidae, Y-tube olfactometer assay, weed control, biological control, host preference Abstract 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: Chrysomeli- dae) 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 spec- trometry (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 treat- ments, 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. parvi- flora 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. Introduction The genus Ludwigia (Onagraceae) is pantropical and dis- tributed in temperate North America as well as in temper- ate Asia (Oziegbe & Faluyi, 2012). Eighty-two species of Ludwigia are divided among 23 sections; 25 of these spe- cies are in record of the Old World along with eight sec- tions (Raven, 1963). A mosaic assembly of Ludwigia species has been noted in South America, where 45 of the 82 species are recorded; the family Onagraceae, including the Ludwigia species, appears to have originated in this continent (Ramamoorthy & Zardini, 1987; Peng, 1989). Ludwigia species are considered invasive throughout the world and are a menace to indigenous plant species (Moody, 1989; McGregor et al., 1996; Holm et al., 1997; Tomita et al., 2003; Caton et al., 2010; Chauhan et al., 2011). Most of the Ludwigia species can block navigation channels and are considered as serious weeds in wet areas, particularly in rice fields (Moody, 1989; Holm et al., 1997; Tomita et al., 2003; Rao et al., 2007). Three species, Ludwigia adscendens (L.) Hara, Ludwigia parviflora Roxb., and Ludwigia octovalvis (Jacq.) Raven (Figure S1), are abundant in rice fields of West Bengal, India, and these weeds are a major impediment to rice production as they compete with rice for resources in fields (Mitra et al., 2019). The genus Altica (Coleoptera: Chrysomelidae) is distributed throughout the world and comprises ca. 250 species (Konstantinov & Vandenberg, 1996; Aslan et al., *Correspondence: E-mail: anandamaybarik@yahoo.co.in © 2020 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 168: 91–104, 2020 91 DOI: 10.1111/eea.12870