Influences of host volatiles on feeding behaviour of the Japanese pine sawyer, Monochamus alternatus

Abstract: Choice and no‐choice feeding assays on the twigs of three host species demonstrated the following feeding preference sequence by Monochamus alternatus: Pinus massoniana > Cedrus deodara > Pinus thunbergii. There were significant differences in the concentrations of α‐pinene, camphene, d ‐limonene, β‐phellandrene, longifolene and β‐caryophyllene in volatiles emitted by twigs among the three species. We tested the effects of six monoterpenes (α‐pinene, β‐pinene, 3‐carene, myrcene, limonene and β‐caryophyllene) added to an artificial diet consisting of bark from P. thunbergii on consumption rates by M. alternatus. The addition of α‐pinene at all four concentrations 0.4, 1.2, 3.6 and 10.8 μl/ml resulted in increases of a twofold greater consumption rate than the control at a concentration of 3.6 μl/ml. Limonene inhibited diet consumption at concentrations >0.4 μl/ml. The concentration of α‐pinene in volatiles emitted by twigs was significantly higher for P. massoniana than for P. thunbergii, whereas the reverse was true for limonene. There were no differences for any of the other host components, suggesting that α‐pinene and limonene may play an important role in the adult's selection and acceptance of suitable and unsuitable feed host. Mixed compounds promoted the consumption of artificial diet at a concentration of 0.4 μl/ml, whereas consumption was inhibited at a concentration of 10.8 μl/ml. There were significant linear correlations (β‐pinene: r² = 0.930, P < 0.05; myrcene: r² = 0.933, P < 0.05) between the amount of diets consumed and diet concentrations of β‐pinene and myrcene. In conclusion, host volatile terpenes may stimulate or repel M. alternatus depending on terpene concentrations they encounter during initial feeding and then possibly inhibit further feeding activity once concentrations increase to threshold levels.