Dioryctria sylvestrella (Lepidoptera: Noctuidae) is a serious pest of the Korean pine (Pinus koraiensis) which is the precious tree species in northeast China. It is a specialist feeder on the Korean pine and can`t complete its life circle on tree species other than Pinus koraiensis. Common pest control measures such as spraying insecticides are normally not effective because their larvae feed inside the pine cones and shoots. Once outbreak, more than 85% trees could be damaged, which might result in significant reduction in seed production. Until now, there is no efficient and environment friendly pest control method to reduce the economic losses caused by this serious pest insect. Macrocentrus sp. is a key larval parasitoid of D. sylvestrella and might play an important role in regulating its host population dynamics as a natural control agent.
Chemical signals play a major role in the orientation of insects to mates and suitable hosts. In this paper, we describe the diurnal behavioral responses of the adult moths and their parasitoid wasps to P. koraiensis cones, shoots and branches by using a Y tube olfactometer. Volatiles released during day and night from cones, shoots and branches of healthy and D.sylvestrella larvae-damaged pine trees were collected and analyzed by GC-MS. The aim of the present study was to determine the diurnal pattern of volatiles released from cones, shoots and branches, and its potential effect on host-finding behavior of D. sylvestrella and the its parasitoid Macrocentrus sp..
Y tube bioassay indicated that virgin, mated female moths and male moths responded strongly to volatiles released from the healthy pine cones and shoots during night. Mated females seemed also to respond to the larvae-damaged cones at night. Whereas the parasitic wasps (both sexes) were more responsive to volatiles released from D. sylvestrella larvae-damaged pine cones and shoots during the daytime. GC-MS analyses showed significant diurnal variations in volatile compositions and contents between healthy and damaged pine samples, and among the cones, shoots and branches, especially in the relative contents of major monoterpenes, including, α-Pinene, Camphene, β-Phellandrene β-Pinene, 3-Carene, Ocimene, Myrcene and D-limonene. D-limonene was only volatilized form lateral branches of P. koraiensis, and the response ratio for males, virgin and mated females of D. sylvestrella to lateral branches were significant lower than cones and tips. Thus, we assumed that D-limonene should play a special function on D. sylvestrella host location of the adult moths. This function would be an important reason of Dioryctria evading the lateral branchs of P. koraiensis. Some specific sequiterpenes such as Bornylacetate and Caryophyllene were present mainly from the D. sylvestrella larvae-damaged pine samples, which might function as repellent volatiles for the moth or attractant volatiles (synomone) for the parasitoid wasps. The host selection behaviors of D. sylvestrella and their parasitic wasps seemed to be regulated or influenced by the variations of monoterpene contents in the pine cones, shoots or branches. The exact functionality of these specific sesquiterpenes (individuals or in combinations) is not known; however, further study is surely needed to determine if these sesquiterpenes with or without monoterpenes might play a role in oviposition behaviors of both D. sylvestrella and their parasitoid wasps.