Abstract:

Abstract: We studied the response of the ladybeetle, Chilocorus kuwanae, to volatiles released by persimmon trees (Diospyros kaki) induced either by an attack of Japanese wax scales, Ceroplastes japonicus, or by an exogenous methyl jasmonate (MeJA) application. Results showed that, when C. japonicus was at the young nymph stage in July, its attack was not able to induce persimmon trees to attract ladybeetles. In the contrast, persimmon trees after sprayed with MeJA displayed a significant attraction to the ladybeetles, which showed a fluctuation rhythm of increase-decrease-increase again. The peaks of attractive responses were 78.21% at 8 h (15:00) and 73.42% at 24 h (7:00 next morning) after the MeJA-treatment. A total of 17 chemical components were detected by GC/MS from the volatiles of MeJA-treated or control persimmon trees. Among those chemicals, 3 terpenoid components were higher in MeJA-treated trees than that in control trees, and 2[1]-pinene and D-limonene were detected only from the volatiles of MeJA-treated persimmon trees. These differences in the volatile compositions suggested the possible reason for the attraction of the treated persimmon trees to the ladybeetles, which was futher confirmed by the ladybeetle attraction experiment with those chemicals. Both D-limonene and α-pinene displayed a significant attractiveness (78.95% and 75.61%, respectively) at concentration of 1×10^-4 and 1×10^-5g mL^-1. Therefore, it is suggested that MGA as a signal transducer may be a potential agent in regulating volatile emissions of the host plant and improving biological control of scale insects. The fluctuation in amounts of terpenoid compounds was also found in the MeJA-treated trees. Up to 8 h after treatment, the relative content of 6 terpenoids all increased, but to the 12 h only 0.87% α-pinene was detected. However to next 7:00 am, the 6 terpenoids were detected again and among them α-pinene even reached 73.01%.

Key words: Key words: Ceroplastes japonicus, Chilocorus kuwanae, persimmon tree, methyl jasmonate, volatiles