Journal of Invertebrate Pathology 94 (2007) 125–129 www.elsevier.com/locate/yjipa 0022-2011/$ - see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2006.09.002 Toxicity of Bacillus thuringiensis -endotoxins against bean shoot borer (Epinotia aporema Wals.) larvae, a major soybean pest in Argentina Diego H. Sauka a,¤ , Jorge Sánchez b , Alejandra Bravo b , Graciela B. Benintende a a Bioinsumos Microbianos, Instituto de Microbiología y Zoología Agrícola, INTA., CC. No. 25 (1712) Castelar, Buenos Aires, Argentina b Instituto de Biotecnología, UNAM, Ap. Postal 510-3, Cuernavaca, 62250 Mor., Mexico Received 2 July 2006; accepted 6 September 2006 Available online 27 October 2006 Abstract The toxicity of seven Bacillus thuringiensis Cry protoxins was tested against neonate larvae of Epinotia aporema, a major soybean pest in Argentina and South America. The most active protoxins were Cry1Ab and Cry1Ac, with LC 50 values of 0.55 and 1.39 g/ml, respec- tively. Cry1Aa, Cry1Ba, Cry1Ca, and Cry9Ca protoxins were equally toxic with LC 50 values about 4 g/ml, whereas Cry1Da was not toxic. The synergistic activity of diVerent protoxin-mixtures was also analyzed, no synergistic eVect between the Cry proteins was observed, with the exception of the poorly toxic Cry1Ba/Cry1Da mixture that was slightly synergistic. The binding capacity of individual Cry1 and Cry9Ca toxins to brush border membranes of E. aporema was also determined. The non-toxic Cry1Da toxin was the only toxin unable to bind to E. aporema membranes. In addition the heterologous competition experiments showed that Cry1Ab and Cry1Ac toxins share a common binding site. Based on these data, we propose that Cry1Ab and Cry1Ac toxins could be used in the biological control of E. aporema.  2006 Elsevier Inc. All rights reserved. Keywords: Bacillus thuringiensis; Epinotia aporema; Cry proteins 1. Introduction The bean shoot borer, Epinotia aporema Wals. (Lepidop- tera: Tortricidae), is an economically important pest of soy- bean and other legume crops including alfalfa, beans, peanut, and chickpea in South America (Villata and Ayessa, 1994). In Argentina, its economic importance has grown due to the increase in the sown soybean area since 1980 (FAOSTAT data, 2006). More than 14 million hect- ares are dedicated to soybean cultures, and this crop takes the Wrst place in the country’s grain exports (SAGPyA data, 2006). During the vegetative and reproductive stages of the crop, E. aporema larvae cause widespread damage in diVer- ent parts of the plant including shoots, sheaths, pods, Xow- ers, leaves, and seeds, causing losses in harvest yields that vary between 7% and 40% in soybean crops, depending on environmental conditions and population levels (Iannone et al., 1987). Currently, broad-spectrum chemical insecti- cides are used to control this pest, delaying or suppressing Weld colonization by natural enemies. This scenario com- promises the implementation of a proper integrated pest management scheme for soybean crops, in areas where the incidence of E. aporema reaches high population levels (Moscardi and Sosa Gomez, 1992). The gram-positive bacterium Bacillus thuringiensis (Bt) 1 is used worldwide as biopesticides for the control of several lepidopteran, coleopteran, and dipteran insect pests (Sch- nepf et al., 1998). The insecticidal activity of Bt is due to crystals of proteinaceous nature (Cry proteins or -endo- toxins) produced during sporulation (Schnepf et al., 1998). Upon ingestion, the crystals are solubilized by the alkaline conditions existing in the midgut lumen of susceptible * Corresponding author. Fax: +54 11 4621 0670. E-mail address: dsauka@cnia.inta.gov.ar (D.H. Sauka). 1 Abbreviations used: Bt, Bacillus thuringiensis; SF, synergism factor; LC 50 , mean lethal concentration.