Identification of relevant non-target organisms exposed to weevil-resistant Bt sweetpotato in Uganda

Abstract

Assessment of the impact of transgenic crops on non-target organisms (NTO) is a prerequisite to their release into the target environment for commercial use. Transgenic sweetpotato varieties expressing Cry proteins (Bt sweetpotato) are under development to provide effective protection against sweetpotato weevils (Coleoptera) which cause severe economic losses in sub-Saharan Africa. Like any other pest control technologies, genetically engineered crops expressing insecticidal proteins need to be evaluated to assess potential negative effects on non-target organisms that provide important services to the ecosystem. Beneficial arthropods in sweetpotato production systems can include pollinators, decomposers, and predators and parasitoids of the target insect pest(s). Non-target arthropod species commonly found in sweetpotato fields that are related taxonomically to the target pests were identified through expert consultation and literature review in Uganda where Bt sweetpotato is expected to be initially evaluated. Results indicate the presence of few relevant non-target Coleopterans that could be affected by Coleopteran Bt sweetpotato varieties: ground, rove and ladybird beetles. These insects are important predators in sweetpotato fields. Additionally, honeybee (hymenoptera) is the main pollinator of sweetpotato and used for honey production. Numerous studies have shown that honeybees are unaffected by the Cry proteins currently deployed which are homologous to those of the weevil-resistant Bt sweetpotato. However, because of their feeding behaviour, Bt sweetpotato represents an extremely low hazard due to negligible exposure. Hence, we conclude that there is good evidence from literature and expert opinion that relevant NTOs in sweetpotato fields are unlikely to be affected by the introduction of Bt sweetpotato in Uganda.

Characterization of the Activity Spectrum of MON 88702 and the Plant-Incorporated Protectant Cry51Aa2.834_16

“…As examples, Cry2Aa (formerly CryB1) is active against insects from the orders Lepidoptera and Diptera (mosquitoes) [22, 23, 58], while Cry3Aa displays activity against insects from the orders Coleoptera, Hemiptera, and Hymenoptera [58]. It is important to know that this cross-order activity does not impact the environmental safety of Bt -based products as Cry proteins tend be highly toxic to one order or closely related orders (primary specificity range), but much less toxic to distantly related taxa [36, 58, 59]. This pattern of activity was observed for the Cry51Aa2.834_16 protein where high toxicity or protection from feeding damage was shown against some hemipterans and thysanopteran species (primary specificity range), but relatively weak toxicity was shown against distantly related Coleoptera species.…”

Invertebrate pests and diseases of sweetpotato (Ipomoea batatas): a review and identification of research priorities for smallholder production

“…In sub-Saharan agriculture the use of transgenic Bt sweetpotato is viewed as an attractive alternative to the slower conventional breeding for host-plant resistance as well as to other pest management options which some consider to be too expensive for smallholder farmers to use (Rukarwa et al, , 2014. Other research using Bt protein expression in sweetpotato has taken place in Cuba (Morán et al, 1998), China (Yang et al, 2011) and India (Shekhar et al, 2013).…”

The Independent Biological Activity of Bacillus thuringiensis Cry23Aa Protein Against Cylas puncticollis

“…Moreover, the efficiency of different Bacillus thuringiensis insecticidal proteins in controlling Cylas spp. has been previously shown (Morán et al, 1998;Ekobu et al, 2010;Rukarwa et al, 2014).…”

“…larvae (Ekobu et al, 2010). Accordingly, it has been demonstrated that coleopteran-active Cry proteins; Cry3Aa3, Cry3Bb3, Cry3Ca1, Cry7Aa1, and Cry23Aa/Cry37Aa proteins are toxic for different sweet potato weevil species (Morán et al, 1998;Ekobu et al, 2010;Rukarwa et al, 2014). More attention has been directed toward the 3-domain group of insecticidal Cry proteins.…”

“…Nowadays, some studies have been performed to identify toxic Cry proteins to Cylas spp. larvae (Ekobu et al, 2010) such as the coleopteran-active Cry proteins; Cry3Aa3, Cry3Bb3, Cry3Ca1, Cry7Aa1, and Cry23Aa/Cry37Aa (Ekobu et al, 2010;Rukarwa et al, 2014). The development and efficiency of Bt transgenic sweet potato carrying a single Bt cry gene have been evaluated (Morán et al, 1998;Rukarwa et al, 2014).…”