Straight-chain alkanes derived from leaf waxes stimulate feeding behaviors in a cucurbit leaf beetle, Aulacophora femolaris (Chrysomelidae, Coleoptera)

Abstract

The importance of plant cuticular waxes in plant–herbivore interactions has become an area of increasing interest, but it has been poorly explored in chrysomelid beetles, one of the most important groups of insect pests. In this study, we investigated the effects of cuticular wax on feeding behaviors of Aulacophora femoralis (Chyrosomelidae), a pest of Cucurbitaceae crops. We analyzed chemical compositions of leaf cuticular waxes using gas chromatography–mass spectrometry. The compositions were significantly different among plant species; in particular, host (Cucumis maxima, C. pepo, C. sativus, Cucurbitaceae) and non-host (Pueraria lobata, Fabaceae) leaves had distinctive compositions of cuticular waxes. We examined if the cuticular wax induces feeding behaviors based on a bioassay using filter papers treated with cuticular wax extract from host or non-host leaves, or a synthetic mixture of straight-chain alkanes (n-alkanes), major components of the host cuticular waxes shared among different host species. We found that the beetles frequently left bite marks on the filter papers treated with n-alkanes but less frequently on those treated with cuticular wax extracts of host leaves. These results indicate that leaf cuticular wax n-alkanes stimulate feeding behavior, but are not cues for host selection.