Systemic Accumulation and Deterrent Effects of Ipomeamarone in Sweetpotato Weevil-Injured Storage Roots

Sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), is one of the most devastating pests of sweetpotatoes in tropical and subtropical regions. Furanoterpenoids are produced when sweetpotato weevils feed on storage roots, making them potentially unmarketable and toxic to livestock and humans. However, accumulation of these furanoterpenoids in uninfested parts of weevil-infested storage roots is poorly characterized. Here we identified ipomeamarone and its precursor, dehydroipomeamarone, in weevil-infested sweetpotato storage roots and confirmed the identities of the compounds by LC-MS, LC-MS/MS, and NMR analysis. Ipomeamarone induction was systemic in the roots, with elevated levels detected in healthy parts of the roots 2-5 cm away from the site of infestation. A clear relationship between the presence of furanoterpenoids in the storage root and the behavior of C. formicarius elegantulus was found. When adults were presented with root slices taken at several distances from the point of infestation, the number of eggs laid increased progressively with distance from the point of infestation, peaking at 7 cm from the site of infestation. Both egg-laying and adult feeding were reduced on isolated root slices treated with pure ipomeamarone, underscoring the potential role of this compound as a deterrent against C. formicarius elegantulus. This study contributes to our understanding of host plant selection and could inform integrated pest management strategies against the sweetpotato weevil.