© 2005 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 114: 161– 169, 2005 161 Blackwell Publishing, Ltd. Effects of Bt maize expressing Cry1Ab and Bt spray on Spodoptera littoralis Anna Dutton, Jörg Romeis & Franz Bigler* Agroscope FAL Reckenholz, Swiss Federal Research Station for Agroecology and Agriculture, Zurich, Switzerland Accepted: 25 October 2004 Key words: Bt expression, Dipel, feeding damage, non-target herbivore, toxicity, transgenic plants, Lepidoptera, Noctuidae Abstract Various studies have been conducted to assess the damage caused by secondary lepidopteran pests to transgenic Bt maize expressing Cry1Ab. However, to date little is known on the effects of transgenic maize on Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae), a polyphagous herbivore which is considered a pest in Mediterranean maize growing areas. Here we present results on the effects of Bt maize (Bt-11) and Bt spray (Dipel) on the various life stage parameters of this herbivore. We further assess the expression of Cry1Ab in different leaves and leaf parts in maize at a given plant growth stage, and determine whether the feeding damage of 3rd instar S. littoralis is influenced by Bt toxin expression. Contrary to previous literature reporting that S. littoralis is not sensitive to Bt Cry1Ab toxin, our results show that insects fed on either transgenic or Bt sprayed plants were nega- tively affected. Young S. littoralis larvae (1st and 2nd instars) were found to be the most sensitive to the Bt toxin. This was represented by a higher mortality and a slower developmental time of larvae maintained on transgenic or sprayed plants when compared to insects maintained on control plants. Moreover, Bt maize had a stronger and prolonged detrimental effect on insects when compared to Bt spray in maize. This was revealed by the fact that insects maintained on transgenic plants from 3rd instar to pupation took longer to reach adult emergence compared to insects that were maintained on sprayed plants. This was likely due to the continuous exposure of insects to the toxin when kept on transgenic maize. ELISA results showed a variation in the amount of Bt toxin among different leaf sections in transgenic maize at a given plant growth stage. These differences in Bt toxin were primarily found in the youngest leaf of growing plants. Although the lowest amounts of Bt toxin were detected in the growing leaf section of young leaves, this difference did not appear to influence the feeding behavior of 3rd instar S. littoralis. Introduction The engineering of plant genes to encode for insecticidal proteins and control insect pests is a modern alternative to chemical insecticides. Maize, Zea mays (L.) (Poaceae), expressing the synthetically modified cry1Ab gene from the soil bacterium Bacillus thuringiensis ssp. kurstaki strain HD-1 (Bt) was the first insect-resistant transgenic crop to be commercialized in 1996 (EPA, 2000). Although transgenic Bt maize was initially developed to control the European corn borer, Ostrinia nubilalis , Bt maize also has the potential to control other lepidopteran maize pests (Pilcher et al., 1997; Lynch et al., 1999; Archer et al., 2000; Binning & Rice, 2002). Seven years after its commercial introduction, Bt maize is planted on an area of 12.3 million hectares world-wide (James, 2003). Some potential drawbacks with the wide adoption of such technology have already been discussed (Wolfenbarger & Phifer, 2000; Conner et al., 2003). These, among other risks, include the potential for the target pest to become resistant to the protein expressed by the transgenic plant, and the risks that these plants pose to non-target arthropods including herbivores, natural enemies, and pollen feeders. Several studies have evaluated the effects of Bt maize on various lepidopteran species. These studies have included an assessment of the effects of different Bt maize events on species which are of importance for either agriculture or * Correspondence: Agroscope FAL Reckenholz, Swiss Federal Research Station for Agroecology and Agriculture, Reckenholzstr. 191, CH-8046 Zurich, Switzerland. Tel. +41 1 377 72 35; Fax: +41 1 377 72 01; E-mail: franz.bigler@fal.admin.ch