Short Communication Spodoptera frugiperda (J.E. Smith) with field-evolved resistance to Bt maize are susceptible to Bt pesticides S.R.K. Jakka 1 , V.R. Knight, J.L. Jurat-Fuentes ⇑ Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996, USA article info Article history: Received 29 April 2014 Accepted 28 August 2014 Available online 8 September 2014 Keywords: Bacillus thuringiensis Bt maize Spodoptera frugiperda Cross-resistance Bt pesticide Bt resistance abstract Field-evolved resistance to maize event TC1507 expressing the Cry1Fa toxin from Bacillus thuringiensis (Bt) was detected in populations of Spodoptera frugiperda from Puerto Rico. We tested for cross-resistance to purified Cry1A toxins and commercial Bt pesticides in susceptible (Benzon) and TC1507-resistant (456) strains of S. frugiperda. Larvae from the 456 strain exhibited cross-resistance to Cry1Ab and Cry1Ac toxins, while no differences in susceptibility to XenTari WG and DiPel ES pesticides were detected. These data support cross-resistance to toxins that share binding sites with Cry1Fa and no cross-resistance to Bt pes- ticides in S. frugiperda with field-evolved resistance to Bt maize. Ó 2014 Elsevier Inc. All rights reserved. The fall armyworm, Spodoptera frugiperda (J.E. Smith) is a devas- tating polyphagous pest that has developed resistance to numer- ous chemical and biological insecticides. Larvae of this insect pest are targeted by transgenic maize event TC1507 expressing the cry1Fa toxin gene from the bacterium Bacillus thuringiensis (Bt) (Siebert et al., 2008). However, intense year-long cultivation together with climatic and geographic conditions led to the evolu- tion of field resistance to event TC1507 in S. frugiperda populations from Puerto Rico (Storer et al., 2010). While the mechanism involved in this case of field resistance has not been reported to date, reduced levels of alkaline phosphatase have been detected in midgut tissue from resistant compared to susceptible S. frugiperda (Jurat-Fuentes et al., 2011). Current models of Cry intoxication in Lepidoptera include a necessary toxin binding step to receptors on the brush border membrane of the host midgut, with alkaline phosphatase being considered as a putative Cry1 toxin receptor (Arenas et al., 2010). The importance of this toxin binding step for susceptibility is highlighted by numerous reports of resistance and cross-resistance due to alterations in binding sites shared by diverse Cry toxins (Ferré and Van Rie, 2002). Con- sequently, the described pattern of cross-resistance to Cry1A toxins in S. frugiperda strains derived from egg masses collected in Puerto Rico (Blanco et al., 2010; Storer et al., 2010; Velez et al., 2013) is in agreement with shared binding sites for Cry1Fa and Cry1A toxins predicted by Cry toxin binding site models in S. frugiperda (Luo et al., 1999). In addition, Cry1Fa-resistant S. frugiperda strains are not cross-resistant to toxins not sharing binding sites with Cry1Fa, including Cry1Ba, Cry2Aa, and Vip3A toxins (Sena et al., 2009), further supporting alterations in shared Cry1Fa–Cry1A toxin binding sites as the mechanism responsible for field resistance to Bt maize event TC1507. During the early stages of Bt crop commercialization it was rec- ognized that, since transgenic Bt crops and Bt pesticides may con- tain the same Cry toxins or toxins that share binding sites in the insect gut, the potential for cross-resistance to Bt pesticides in insects that develop resistance to Bt crops exists (Federici, 1998). Thus, exposure to Bt pesticides was suggested as a factor involved in development of S. frugiperda resistance to Bt maize in Puerto Rico (Storer et al., 2012). Cross-resistance to Bt pesticides would greatly reduce S. frugiperda control options, especially for organic farmers who rely heavily on Bt pesticides for insect control. The availability of S. frugiperda with field-evolved resistance to Bt maize allowed us to assess of the risk of cross-resistance to Bt pes- ticides. We tested cross-resistance to two commercially-available Bt pesticides targeting S. frugiperda larvae in a strain of S. frugiperda (strain 456) with field-evolved resistance to TC1507 maize. This strain was originated from isofamilies derived from egg masses collected at maize fields in Puerto Rico that displayed high levels of resistance to Cry1Fa and cross-resistance to Cry1Ac (Blanco et al., 2010). We have maintained this strain for more than 30 http://dx.doi.org/10.1016/j.jip.2014.08.009 0022-2011/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. Address: Department of Entomology and Plant Pathol- ogy, 370 Plant Biotechnology Building, 2505 E. J. Chapman Drive, Knoxville, TN 37996, USA. Fax: +1 (865) 974 4744. E-mail address: jurat@utk.edu (J.L. Jurat-Fuentes). 1 Current Address: Department of Entomology, Iowa State University, Ames, IA 50011, USA. Journal of Invertebrate Pathology 122 (2014) 52–54 Contents lists available at ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip