## 5 Alkaline Foreguts Do Not per se Render Animals Vulnerable to Bt Toxins  
Most concerning are the assertions in [PERSON]'s paper that \"_the presence of an alkaline gut pH makes foreign-fermenting mammals, metamorphosing tadpoles, and certain orders of insects susceptible to gut damage by Bt and related insecticidal toxins_\" and \"_an alkaline gut, however, renders animals susceptible to the action of toxins produced by Bacillus thuringiensis and Lysinibacillus sphareicus_\". Alkaline guts alone are, clearly, not sufficient to induce host sensitivity, as evidenced above. A critically important oversight of [PERSON]'s assertions are that he ignores the vast literature that shows receptor dependence for pesticidal proteins [30] and that mutation of receptors can render normally susceptible species resistant (e.g., [31; 32]). This renders animals lacking receptors, like most invertebrates and vertebrates, insensitive to the toxins. In reality, Bt pesticidal proteins kill only a narrow range of targets. Moreover, this level of selectivity can mean that even insects within a small taxonomic subgroup can show variable susceptibility. For example, Cry4 Ba is toxic against the mosquitoes _Aedes aegypti_ and _Anopheles stephensi_ but not _Culex pipiens_[33]; Cry48 Aa1/Tpp49 Aa1 are toxic to _Culex quinquefasciatus_, _An. stephensi_ and _Aedes albopictus_ but not against _Anopheles gambiae_ or _Ae. aegypti_[34; 35]; Tpp1/Tpp2 kill _Aedes atropalpus_ but have very limited to no effect against _Ae. aegypti_[36]. Beyond receptors, the proteinase susceptibility of individual toxins, along with the proteinase arsenal of the gut, are also important factors, independent of whether the gut is acidic or alkaline. Thus, Cry3 proteins degrade rapidly in simulated gastric juice [37] but are still able to exert toxicity in the acidic guts of target beetles, and changes in proteinase activity can lead to reduced Cry3 Aa susceptibility [38]. Some individual toxins may also be proteolytically activated in different ways with consequent effects on target range [39]. The extent of safety tests is also brought into question, stating that tests were carried out on animals such as rats and mice, but ignoring the copious other tests and exposures that have been assessed. Mammalian safety tests on Bt products have a long history [40] and, contrary to what is stated in the publication, their effects on ruminants have been analysed. For example, with respect to ungulate mammals with alkaline foreguts, testing of Bt strains in direct feeding to sheep found no adverse consequences [41; 42]. As a result, the safety risks of Bt and its toxins implied by [PERSON] are simply not upheld given the evidence available. It is important to note the use of genetically modified crops expressing Bt proteins (particularly maize and soybeans) has increased since their first approval in 1995 [43] to the point that approximately 80% of the areas cultivated for both corn and cotton in the USA are sown with Bt products [44]. These crops have regularly been used as primary feeds for poultry, pigs, dairy and beef cattle in North America and Brazil for over 20 years, yet no adverse effects have been reported [45; 46]. Use as feeds on such a scale in these countries would certainly have been expected to show significant effects if such effects existed in these major markets.