Chemical factors influencing the feeding preference of three Aulacophora leaf beetle species (Coleoptera: Chrysomelidae)

Three cucurbitaceous feeding leaf beetle species, Aulacophora indica, A. lewisii, and A. nigripennis, were investigated with regard to the relationship between feeding preference by the beetles and cucurbitacins B, E, I, and E-glucoside contents in the leaves of 18 cucurbitaceous plant species. HPLC analysis and TLC analysis of A. lewisii revealed that the cucurbitacin B and E-glucoside, which are strong feeding stimulants for A. indica and A. lewisii, were abundant in Lagenaria siceralia, Sicyos angulatus, and Cucumis melo leaves. In a feeding preference test using fresh leaves, A. indica preferred various cucurbitaceous plant species and methanol extracts regardless of the contents of the four cucurbitacins. A. lewisii mostly fed on Luffa cylindrica leaves in which the four cucurbitacins were not detected. A. lewisii was also stimulated to feed by the methanol extracts of Lagenaria siceraria and L. cylindrical, while A. nigripennis, which is only slightly stimulated to feed by the four cucurbitacins, fed primarily on Trichosanthes kirilowii var. japonica leaves. Among 18 cucurbitaceous plants, only Diplocyclos palmatus leaves were completely rejected by the three beetle species, and these beetle species did not even feed on D. palmatus leaves treated with the cucurbitacins. These results indicate that some leaf constituents as well as the four cucurbitacins play an important role in host plant selection by the three cucurbitaceous feeding beetle species.