Nonanoic acid, other alkanoic acids, and related compounds as antifeedants in Hylobius abietis pine weevils

Abstract

A medium‐length, straight‐chain alkanoic acid, nonanoic acid, is known from laboratory microassays to be an antifeedant in adults of the large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae). Our hypothesis was that we could find new, less volatile alkanoic acids or related compounds suitable for field application and with improved long‐term duration. Alkanoic acids of varying chain lengths (C6–C13) were tested for antifeedant activity in H. abietis adults. Microassay choice tests showed that straight‐chain (C6–C11) alkanoic acids were active. However, high activities were restricted to the (C6–C10) acids, with the C9 (nonanoic acid) at 4 µmol cm−2 being the most active one. In a no‐choice test on pine twigs, the antifeedant effect of C10 acid was lower than that of the C8 and C9 acids. In microassays, less volatile methyl‐branched alkanoic acids exhibited lower antifeedant activities than did the corresponding straight‐chain ones. However, the most active of the methyl‐branched acids, 2‐methyldecanoic acid, had an activity similar to that of nonanoic acid. Compounds related to nonanoic acid were either active (1‐nonanol), weakly active (nonanoic anhydride), or inactive (nonanal, sodium nonanoate). The anhydride was highly active in the microassay, but less active on twigs. The antifeedant effects of the straight chain (C8–C10) alkanoic acids against pine weevil feeding were tested in the field. In contrast to the results from the twig tests, the less volatile C10 acid was more active in the field for the protection of transplants on fresh clear cuts over a 3‐month period than both the C8 and C9 acids. Phytotoxic effects of the alkanoic acids were observed both in the field and in laboratory studies. If a protective layer of paraffin was applied to the stem prior to application of the alkanoic acids, these undesired side effects were reduced.

Antifeedants and Feeding Stimulants in Bark Extracts of Ten Woody Non-host Species of the Pine Weevil, Hylobius abietis

“…Similar to our results, the compound exhibited antifeedant activity against the weevil when tested in a feeding bioassay (Borg-Karlson et al 2006). In accordance with the decreased antifeedant activity found for carboxylic acids with chains longer than C10 (Månsson et al 2006), no antifeedant activity was found for hexadecanoic-, linoleic-, or linolenic acids that were present in almost all extracts (Table 1).…”

“…We found only hexanoic acid in the pentane bark extracts of Ilex and Alnus, and nonanoic acid in the pentane bark extract of Ilex (Table 1). Thus, the feeding avoidance of H. abietis on the ten woody species investigated in this work is not fully explained by the presence of these carboxylic acids, as it was for linden (Månsson et al , 2006.…”

“…The content of known antifeedants, such as straightchained aliphatic carboxylic acids in the range C6-C9 (Månsson et al 2006), carvone, and carvacrol (Schlyter et al 2004b) in the 20 extracts was determined by GC-MS (Table 1). Among known active carboxylic acids, the feeding deterrents hexanoic acid (in the pentane extract of Ilex and Alnus) and nonanoic acid (in the pentane extract of Ilex) were detected.…”

“…We previously showed that some aliphatic carboxylic acids (in the range C6-C10) act as antifeedants against the pine weevil (Månsson et al , 2006. Of these, nonanoic acid was found in a dichloromethane/methanol bark extract of Tilia (Månsson 2005;Månsson et al 2005).…”

“…Several analogues of nonanoic acid are also active antifeedants (Månsson et al 2006). While reports of the occurrence of similar carboxylic acids in bark tissue are sparse, several have been found in other tissues from some of the 11 woody species (Nahrstedt et al 1981;Buttery et al 2000).…”