Individual and synergistic toxicity of solanaceous glycoalkaloids against two coleopteran stored-product insects Gomah Nenaah Received: 31 March 2010 / Accepted: 25 August 2010 / Published online: 10 September 2010 Ó Springer-Verlag 2010 Abstract Toxicity of solanaceous glycoalkaloids against stored-grain insects was investigated under laboratory conditions. The total glycoalkaloids (TGAs), a-chaconine and a-solanine from potatoes, Solanum tuberosum L. and a-tomatine from tomatoes, Lycopersicon esculentum Mill. were isolated and tested in this bioassay. Their acute and residual toxicity were assessed against the rust red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebri- onidae), and the rice weevil, Sitophilus oryzae L. (Cole- optera: Curculionidae). All compounds were tested either individually or as binary mixtures. Results revealed con- siderable toxicity of the tested glycoalkaloids against the target insects. When adults of S. oryzae were exposed to a dry-film residue of these phytochemicals, the total gly- coalkaloids (TGAs) fraction was the most toxic, followed by a-solanine, a-chaconine, and a-tomatine with LC 50s of (38.6 and 22.1), (48.2 and 38.9), (52.00 and 41.6), and (82.3 and 67.00) lg/cm 2 at 24 and 48 h post-treatment, respectively. The order of toxicity against T. castaneum in a descending order was TGAs [ a-chaconine [ a-sola- nine [ a-tomatine. All compounds were more toxic when insects were fed grains treated with these phytochemi- cals (LC 50s of TGAs were 7.4 and 16.2 mg/kg grains at 48 h post-treatment against S. oryzae and T. castaneum, respectively. All compounds, particularly the TGAs, exhibited promising residual toxicity effects. Toxicity of glycoalkaloids was exceeded when tested as binary mix- tures indicating their synergistic interaction. The study recommends the use of glycoalkaloids of Solanaceae as biorationals and natural leads to protect stored grains from insect infestation. Keywords Bioinsecticides  Glycoalkaloids  Stored-grain insects  Synergistic effect Introduction There are well-documented toxic hazards and environ- mental drawbacks associated with the massive application and the excessive reliance on broadly toxic chemical pes- ticides in controlling insect pests (Prakash and Rao 1997; Kim et al. 2003; Kljajic ´ and Peric ´, 2005; Isman 2007; Da- glish 2008). The development of genetically resistant strains of insects and the prohibitive costs of conventional insec- ticides have become major concerns and have given impetus to the search for new alternatives for pest management (Obeng-Ofori and Reichmuth 1999; Kim et al. 2003; Isman 2006, 2007; Yuya et al. 2009; Seffrin et al. 2010). Higher plants, undoubtedly, represent a good alternative approach for pest management. They constitute a rich source of bioactive compounds that are biodegradable into non-toxic products and potentially suitable for use, espe- cially against insects of stored grains. Recently, many of the plant-derived materials were extensively tested as insecti- cides against insects of stored products alone or as mixtures with natural products such as diatomaceous earth (Park et al. 2003; Cox 2004; Athanassiou et al. 2004, 2005, 2007; Han et al. 2006; Kavallieratos et al. 2007; Rozman et al. 2007; Ogendo et al. 2008; Lo ´pez et al. 2008; Cosimi et al. 2009). Communicated by C.G. Athanassiou. G. Nenaah Zoology Department, Faculty of Science, Kafrelsheikh University, Kafrelsheikh, Egypt G. Nenaah (&) Biology Department, College of Arts and Science, Najran University, P.O. Box 1988, Najran, Saudi Arabia e-mail: gnenaah2000@yahoo.com 123 J Pest Sci (2011) 84:77–86 DOI 10.1007/s10340-010-0329-y