## 3 Discussion  
Although _A. grandis_ is currently one of the most devastating cotton insect pests in Brazil and other cotton crop-producing countries, there is little information about which Bt insecticidal proteins are effective against this insect pest [12; 13; 14]. The toxins usually described as active against insects of the order Coleoptera are those of the Cry3, Cry7, Cry8, Cry10, and Gpp34/Tpp35 classes [9; 14], although other classes can be toxic as well, including the Cry1 class. Particularly, the Cry1 Ba6 [16], Cry8 Ka5 [17], Cry1 Ia [18; 19], Cry1 Ia12 [20; 21], and Cry10 Aa [22] proteins have already been proven as toxic to CBW larvae in bioassays using purified recombinant protein or virus-infected insect extracts, while the Cry1 Ia12 [20], Cry1 Ia [19], and Cry10 Aa [11; 13] proteins were also confirmed to show some toxic activity when used in transgenic cotton lines. It is important to highlight that studies evaluating the toxicity of single insecticidal proteins from Bt are required to show which proteins are effective against _A. grandis_. Furthermore, additional studies indicating whether it is suitable to combine the selected proteins in the same transgenic crop will be desirable to avoid the occurrence of cross-resistance among these proteins [23]. Results from the selective bioassay showed that although the survival of the larvae was affected after the ingestion of an artificial diet containing Cry1 Ac, Cry1 Ba, and Cry7 Ab proteins, the highest dose used (100 \(\mu\)g\(\cdot\)g\({}^{-1}\)) caused less than 50% mortality. The results obtained indicate that these proteins have low toxicity towards _A. grandis_ larvae. The Cry1 Ac is a protein known to be toxic to lepidopteran agricultural pest species such as _Helicoverpa zea, Heliothis virescens_[24], _Helicoverpa armigen_[25], _Anticarsia gennmatalis_, and _Chrysodeixis includens_[26], among others. For Coleopterans, although toxicity has been reported for some species [27], studies demonstrating high susceptibility to Cry1 Ac are rare. Therefore, given the expression levels of Cry1 Ac in commercial varieties, with a maximum of 7 and 20 \(\mu\)g\(\cdot\)g\({}^{-1}\) of fresh and dry leaf tissue, respectively [28; 29], our results indicate that these current commercial varieties would not be able to control _A. grandis_. Cry1 Ba was included in this study because it has been described as a protein that has dual activity (toxicity to both Lepidopteran and Coleopteran insects) [14; 30]. A previous study that tested the toxicity of Cry1 Ba on _A. grandis_ established an LC\({}_{50}\) of \begin{table}
\begin{tabular}{c c c c c c} \hline
**Bt Protein** & **n** & **Slope (\(\pm\)SE)** & **LC\({}_{10}\) (FL\({}_{95}\))** & **LC\({}_{50}\) (FL\({}_{95}\))** & \(\chi^{2}\) (d.f.) \\ \hline Cry1 Ac & 841 & 0.58 (0.16) & 2.01 (0.04–7.70) & 317 (188–3378) \({}^{*}\) & 2.08 (5) \\ \hline Cry1 Ba & 840 & 0.43 (0.11) & 0.33 (0.01–1.84) & 293 (92–4486) \({}^{*}\) & 2.05 (5) \\ \hline Cry7 Aa & 841 & 0.35 (0.12) & 0.38 (0.01–3.05) & 1598 (233–ND) \({}^{*}\) & 4.60 (5) \\ \hline Mpp23 Aa/Xpp37 Aa & 735 & 3.80 (0.47) & 0.08 (0.04–0.12) \({}^{*}\) & 0.18 (0.13–0.22) & 4.43 (4) \\ \hline \end{tabular} n = number of evaluated larvae; slope = dose–response quickness; SE = standard error of the mean; LC\({}_{10}\) and LC\({}_{50}\) = concentration that killed 10% and 50%, respectively; FL\({}_{95}\) = 95% fiducial limits; d.f. = degrees of freedom; ND = not determined; \({}^{*}\) value interpolated because they were out of the range of assayed concentrations.  
\end{table} 
Table 1: Parameters estimated by probit analysis from the bioassays with _A. grandis_ larvae tested with several Bt proteins. Toxin concentrations are given in \(\mu\)g of protein per\(\cdot\)g\({}^{-1}\) of artificial diet. 380.8 \(\upmu\)g\(\cdot\)g\({}^{-1}\)[16], which is in line with our results.