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.
Highlights
Sweetpotato (Ipomoea batatas (L) Lam.) is an important crop in all tropical areas of the world
In Uganda Cry proteins were tested for activity against the African sweetpotato weevil resulting in the identification of three samples of Bacillus thuringiensis (Bt) endotoxins, Cry7Aa1, ET33/34 and Cry3Ca1 which were found to be active against C. puncticollis and C. brunneus in artificial diet assays (Ekobu et al 2010)
Based on the considerations addressed on the identification of the functional groups of arthropods associated with sweetpotato fields and categorisation of non-target organisms (NTO), focal species need to be selected from each functional category of NTO group
Summary
Progress in breeding weevil-resistant cultivars has been slow due to the genetic complexity of the crop (hexaploid and highly heterozygous) and lack of attractiveness of deep-rooting varieties which is the most effective breeding target to avoid weevil infestation (Stathers et al 2003). Another option could be to breed for enhanced accumulation of the biochemical component of resistance of the variety New Kawogo, but its inheritance and impact on nutritional quality of the storage roots remain to be elucidated (Stevenson et al 2009). Environmental risk assessment of a Bt crop considers the impact of the Cry protein on the target pest, and on non-target organisms either directly or indirectly (OECD 2007). Non-target risk assessment is a process based on scientific principles that aims at the evaluation of the potential adverse effects of transgenic plants on the non-target organisms of environmental relevance (OECD 2007; Romeis et al 2008)
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