Behavioural responses of Dendrolimus superans and Anastatus japonicus to chemical defences induced by application of jasmonic acid on larch seedlings

Jasmonic acid (JA) is a plant hormone that plays a key role in the interactions between plants, herbivores and herbivore parasitoids. To determine the effect of JA-induced larch defence, two-year-old seedlings of Larix gmelinii (Rupr.) Kuzen. (LG) and Larix olgensis Herry (LO) were sprayed with different concentrations of JA. The effects of these treatments on behavioural responses of the moth, Dendrolimus superans Butler (DS), and its egg parasitoid Anastatus japonicus Ashmead (AJ) were tested by using cages and Y-tube olfactometers. The results showed that the numbers of DS eggs laid on JA-treated seedlings were lower than on control seedlings. The moth (DS) displayed a negative approach response to JA-treated seedlings (P<0.05), and the parasitoid (AJ) showed a positive approach response to the treatments (P<0.05). JA application to larches affected the behavioural responses of DS and AJ for at least five days. The two species of larch had a different stimulus response to JA treatments. The LG seedlings sprayed with low-concentration JA effectively repelled female DS, while LO seedlings which received a high concentration of JA strongly repelled female DS. When sprayed with high-concentration JA, both larch species strongly attracted female AJ. It is implied that in the future, JA application technique could be a new way to control larch herbivore pests and to utilise their parasitoids.