J Pest Sci (2008) 81:9–15 DOI 10.1007/s10340-007-0175-8 123 ORIGINAL PAPER Assessing toxicity of post-emergence herbicides to the Spilarctia obliqua Walker (Lepidoptera: Arctiidae) Garima Gupta · A. K. Bhattacharya Received: 14 December 2006 / Revised: 23 May 2007 / Accepted: 21 June 2007 / Published online: 19 July 2007  Springer-Verlag 2007 Abstract The lethal and sublethal eVects of three post-emergence herbicides, 2,4-D ethyl ester (Weedkill 80WP), imazethapyr (Pursuit 10EC) and quizalofop ethyl (Tergasuper 5EC) fortiWed with artiWcial diets were studied on larvae of Spilarctia obliqua Walker (Lepidoptera: Arctii- dae). Quizalofop ethyl and imazethapyr caused signiWcant reduction of pest survival at almost all levels; however, 2,4-D ethyl ester was nontoxic. Interestingly, LC 50 data (0.230 and 0.855% for quizalofop ethyl and imazethapyr, respectively) obtained from probit analysis were almost equal to labeled doses (x) of quizalofop ethyl (x = 0.16%) and imazethapyr (x = 0.625%), which shows the high toxicity of these compounds against S. obliqua larvae. Among the three herbicides, imazethapyr caused sublethal eVects on this pest, increasing the larval period at almost all concentra- tions tested in the artiWcial diet. Considering the markedly signiWcant eVect of quizalofop ethyl on pest survivorship with no sublethal eVect, we suggest incorporating it into the integrated pest management module for S. obliqua in legumes or oilseed crops with other biorational insecticides. Based on toxicity, imazethapyr can be a potential candidate for integrated management of S. obliqua. However, because of its sublethal eVects, we advocate caution while using it in the presence of pest infestations. Keywords 2,4-D Ethyl ester · Herbicides · Imazethapyr · Quizalofop ethyl · Spilarctia obliqua Introduction Spilarctia obliqua Walker (Syn: Spilosoma obliqua) (Lepidoptera: Arctiidae), commonly known in Asia as the Bihar hairy caterpillar, is a polyphagous pest of numerous important crops, including vegetables, legumes, oil seeds and medicinal plants. It occurs in Bangladesh, Myanmar, India, Pakistan and Sri Lanka (Bhattacharya and Rathore 1977; Nagia et al. 1990; Bhadauria et al. 2001; Goel et al. 2004). The most damaging stage of this pest is the caterpillar, which feeds gregariously during the early (Wrst to third instar) larval stages and solitarily in late (fourth to Wfth instar) larval stages. Indiscriminate use of toxic insecticides for the management of this pest (Kundu 1991; Jaglan and Sircar 1997) causes envi- ronmental pollution, hazards to beneWcial organisms, and development of resistance (Perry et al. 1998). Consequently, a comprehensive integrated pest management (IPM) program is needed to reduce insecticide usage (Luckman and Metcalf 1994). In this study, we investigate the potential use of post- emergence herbicides for management of S. obliqua. Herbicides are a class of pesticides that are marketed spe- ciWcally for the purpose of killing or inhibiting the growth of weeds. However, overlapping eVects of herbicides have been reported on fauna due to soil and water contamination (Fowlkes et al. 2003). Direct toxicity to arthropods (Messersmith 1995; Xu et al. 1997; Chen et al. 1999a, b) and beneWcial insects (Ingram et al. 1947; Uygan et al. 1994; Stadler et al. 1996) was observed in some cases. Her- bicides combined with insecticide can cause additive and synergistic eVects on insect mortality (Ying et al. 2002; Greenberg et al. 2004; Pankey et al. 2004; Schuler et al. G. Gupta (&) Department of Entomology, University of Minnesota, 230 Hodson Hall, 1980 Folwell Avenue, St Paul, MN 55108, USA e-mail: gari_g79@yahoo.com G. Gupta · A. K. Bhattacharya Department of Entomology, Govind Ballabh Pant University of Agriculture and Technology, Pantnagar, Uttaranchal 263145, India