Effects of hydroxycinnamic acid esters on sweetpotato weevil feeding and oviposition and interactions with Bacillus thur
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ORIGINAL PAPER
Effects of hydroxycinnamic acid esters on sweetpotato weevil feeding and oviposition and interactions with Bacillus thuringiensis proteins Milton O. Anyanga1,2 · Dudley I. Farman2 · Gorrettie N. Ssemakula1 · Robert O. M. Mwanga3 · Philip C. Stevenson2,4 Received: 1 February 2020 / Revised: 28 October 2020 / Accepted: 3 November 2020 © The Author(s) 2020
Abstract Sweetpotato weevil (SPW) pest management is challenging because the pest target is sub-terranean, so the application of pesticides is impractical and usually ineffective. Host plant resistance and the genetic transformation of sweetpotatoes to produce entomotoxic Bt proteins offer potential for environmentally benign pest control. Resistance can be conferred by naturally occurring hydroxycinnamic acids which protect against oviposition by adults, but these compounds are restricted to the root surface so do not protect against the cortex bound larvae where the greatest damage occurs. Resistance could be enhanced if combined with expression of Bt proteins in transformed plants, but interactions between hydroxycinnamic acids and Bt proteins remain unknown. Here the bioactivity of Cry7Aa1 protein and hydroxycinnamic acid esters was evaluated individually and in combination against SPW larvae and mortality determined. Low and high concentrations of hydroxycinnamic acid esters alone caused significantly higher mortality of both weevil species in all experiments compared to the control. SPW larval mortality was greater when tested as a combination of hydroxycinnamic acid esters and Bt protein, but this effect was additive not synergistic. Although we report no evidence of antagonistic interactions, the antifeedant effects of the plant compounds conferring host plant resistance could have reduced consumption of the Bt protein in our assays leading to a lower efficacy when combined. Further work is required to determine whether the toxic effects of Bt proteins function alongside host plant resistance in sweetpotato under field conditions. Keywords Bt-proteins · Chlorogenic acid · Cylas puncticollis · C. brunneus · Hydroxycinnamic acid esters · Sweetpotato weevil · Host plant resistance · Nature-based solutions
Key message • Host plant resistance and GM crops provide alternatives
to synthetic pesticides for controlling pests of sweetpotato, but their interactions in combination are unstudied.
Communicated by M. Traugott. * Philip C. Stevenson [email protected] 1
National Crops Resources Research Institute (NaCRRI), P.O. Box 7084, Kampala, Uganda
2
Natural Resources Institute, Chatham Maritime ME4 4TB, Kent, UK
3
International Potato Center (CIP), P.O. Box 22274, Kampala, Uganda
4
Royal Botanic Gardens, Kew TW9 3AB, Surrey, UK
• Hydroxycinnamic acid esters were shown to mediate
resistance, but cortex concentrations were too low to protect against damage by larvae. • Bt protein was bioactive against sweetpotato weevil larvae so could compliment the effects of hydroxycinnamic acids. • Bt protein and hydroxycinnamic acids
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