Effects of hydroxycinnamic acid esters on sweetpotato weevil feeding and oviposition and interactions with Bacillus thuringiensis proteins

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.

Untargeted metabolomics profiling of oat (Avena sativa L.) and wheat (Triticum aestivum L.) infested with wheat stem sawfly (Cephus cinctus Norton) reveals differences associated with plant defense and insect nutrition

“…Hydroxycinnamic acid esters in plant tissues have a direct effect on plant resistance and can decrease oviposition and have a negative effect on larval mortality ( Anyanga et al., 2021 ). They can also form polymers with polyamines to form hydroxycinnamic acid amines (HCAAs) which are deposited in the cell wall near regions of pathogen infection or wounding by boring insects, a process that is associated with strengthening of cell walls and increased resistance ( Grandmaison et al., 1993 ; Facchini et al., 2002 ; Barros-Rios et al., 2011 ; Gunnaiah et al., 2012 ).…”

Tailoring IPM plans to fight a cloaked pest: helping smallholder farmers combat the sweetpotato weevil in sub-Saharan Africa

“…Bacillus cereus biovar. thuringiensis (Bt), the most common bacterial species used in microbial insect control, typically is only pathogenic to the larval stages of SPW (Anyanga et al 2021;Hernández-Martínez et al 2014). The cryptic lifestyle of the SPW, which spend all of their immature stages inside a plant, make delivering bacterial agents difficult and largely ineffective.…”

Breeding for Resistance to the African Sweetpotato Weevils, Cylas puncticollis and Cylas brunneus in Uganda: A Review of the Current Progress

“…Recently, Anyanga et al [81] studied the effect of combining the anti-feedant effects of HCA esters with expression of Bt proteins in transformed plants. The study observed that although resistance was naturally conferred by HCA acids, and deterred oviposition by adults, these compounds were restricted to the roots and did not protect against the larvae, which feed in the cortex, causing the greatest damage.…”