| Pine wood wilt is a devastating epidemic disease in China that infests pine trees in coniferous forests caused by the pine wood nematode (Bursaphelenchus xylophilus). Short-distance natural diffusion of pine wood nematode disease primarily depends on the flight and feeding of its vectors, the Japanese pine sawyer beetle (Monochamus alternatus Hope)(Coleoptera:Cerambycidae). Adult M. alternatus beetles emerge in early summer. They feed on fresh branches of healthy trees until they are sexually mature. The beetles copulate repeatedly and then females lay their eggs under the bark of weak or stressed host trees. The parasitoid beetle Dastarcus helophoroides (Fairmaire)(Coleoptera:Bothrideridae) is an important parasite of longicorn beetles (Cerambycidae). Tetrigus lewisi Candezeis is a predatory click beetle that can feed on M. alternatus. In this research we focused on the volatiles released by pines in different infection stages, volatiles released by other broad-leaf trees (Cinnamomum camphora, Liquidambar formosanat, Broussonetia papyrifera, Dalbergia hupeana, Albizia julibrissin and Sassafras tzumu) in the same plant community; ecological niche of larvae M. alternatus and its nature enemies on pines in different infection stages; as well as electroantennogram and behavior responses of M. alternatus and D. helophoroides to the above volatiles. Main conclusions are as follow:1. The ecological niche and the population distribution of larvae M. alternatus and its nature enemies on P. massoniana and P. thunbergii in different infection stages were investigated:no sign of M. alternatus was observed on pines in the HW stage. The current year oviposition scars were observed on pines in the IP stage, while ecological niche of the current year larvae was low. A great number of the current year oviposition scars were observed on pines in the EP till the PP stages, and ecological niche of the larvae reached maximum within those stages. The ecological niche of M. alternatus was significantly related with the ecological niche of T. lewisi. No D. helophoroides was found on the30infection pines that were investigated.2. Volatiles released by P. massoniana and P. thunbergii in different infection stages were collected and measured:total mass of the volatile decreased as the pines became weaker, it was extremely few at the stages of PP and TP. At the stages of IP and EP, the mass of limonene and3-carene released by the masson pines and leaves of the black pines showed increasing trend, same with a-pinene released by stem of the black pines. After infection with PWN, the major volatile compounds of stems of P. massoniana and P. thunbergii included α-pinene, β-pinene, limonene and3-carene, the major volatile compounds of leaves and branches were a-pinene, β-pinene, limonene,3-carene and β-phellandrene. Within the volatiles released by stems of the pines in HW to MP stage, the percentage of α-pinene increased, the percentage of β-pinene decreased, the percentage of limonene,3-carene increased then decreased; while within the volatiles released by leaves and branches of pines from the HW to MP stage, the percentage of3-carene and β-pinene increased, the percentage of a-pinene decreased, the percentage β-pinene remained.3. EAG responses and behaviour orientation of M. alternatus towards volatiles released by host and non-host trees were tested:the following compounds elicited positive responses in both EAG and behaviour responses,3-carene,(R)-(+)-a-pinene,(S)-(-)-a-pinene, camphene,(R)-(+)-limonene,(S)-(-)-limonene, β-phellandrene, β-myrcene (released by both infection black pine and broad-leaf trees), linalool, cis-3-hexene-l-ol and methyl salicylate (released by broad-leaf trees). Female beetles showed positive responses to α-terpinene,(-)-α-cedrene (released by infection black pine) and (-)-β-caryophyllene (released by both) in behaviour tests. Both genders showed repellent action towards camphor, octanal, ocimene and α-farnesene (released by broad-leaf trees). Results indicted that volatiles from both host and non-host tress could affect the behaviours and actions of M. alternatus.4. The electroantennogram (EAG) technique and a dynamic two choices olfactometer were used to measure the responses of male and female D. helophoroides to the selected synthetic host-related plants volatiles. Significant dose-dependent EAG responses were elicited by nonanal, octanal cis-3-hexen-l-ol (released by broad-leaf trees),3-carene,(R)-(+)-α-pinene,(S)-(-)-α-pinene,(R)-(+)-limonene and (S)-(-)-limonene released by both infection black pine and broad-leaf trees) in both genders. D. helophoroides were attracted by nonanal, octanal cis-3-hexen-l-ol,3-carene,(R)-(+)-α-pinene,(S)-(-)-α-pinene,(R)-(+)-limonene and (S)-(-)-limonene at certain concentration, and repelled to cis-3-hexen-l-ol at the concentration of10-1mg/mg in the behavior bioassay. The results of this study have represented an initial attempt to demonstrate the electrophysiological sensitivities and orientation behaviors of D. helophoroides to the selected host-related plant volatiles.5. Mate recognization and oviposition site detection of M. alternatus were observed and focused on the major functional sensilla involved:antenna, maxillary and labial palps played key roles in mate recognization; while antenna, maxillary and labial palps, the8th abdomen together with the ovipositor all involved with the oviposition site detection behaviors. The morphology, typology and fine structures of sensilla located on antenna, maxillary palp, labial palp and ovipositor were observed systematically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Seven types of sensilla were identified on the antenna, six types were found on the maxillary and labial palps, and five types were found on the8th abdomen and ovipositor. Important sensillar characters such as forms of the socket, connections with the antenna cuticle, openings of the sensillar cuticle (pores, spoke channels or uniporous tip) and varied dendrite structures in the outer dendritic segment were observed. The putative functions including mechanoreception, chemoreception and hygro-or thermo reception of those sensilla were compared and discussed.6. The antennal morphology and sensillar ultrastructure of D. helophoroides and T. lewis were observed:four types of antennal sensilla were found on D. helophoroides; ultrastructural studies revealed porous structures on the cuticle wall and dendritic branches in the inner lumen of Tr.l, Tr.2, Ba.l, and Ba.2, thereby suggesting chemoreception function. Eight types of sensilla were observed on the antennae of T. lewisi, including sensilla chaetica, sensilla basiconica, sensilla trichodea, as well as sensilla auricillica, sensilla coeloconica, sensilla campaniformia, sensilla styloconica and Bohm’s bristles; the chemoreception, mechanoreception and thermo-/hygro-reception functions were deduced from fine structures on the cuticular walls and the dendrites of different sensilla types.The relationship among plants, herbivorous insects, and its natural enemies in the aspect of semiochemical communication in mingled forest have been studies in this thesis.(1) M. alternatus and its parasitoid beetle D. helophoroides could both be attracted by volatiles released by infected black pines (3-carene, limonene, a-pinene), and a common green leaf volatile-cis-3-hexen-l-ol, thus D. helophoroides could locate M. alternatus by approaching the above chemicals.(2) D. helophoroides could also be attracted by nonanal and octanal which released by lots of plants, that increased the possibility of successful parasitism on other hosts.(3) M. alternatus could recognize and response as attracting or repellenting towards different compounds released by6species of non-host broad-leaf trees; those volatiles would interfere the host location of M.alternatus; the mingled pine forest with complex semiochemical information would possess higher resistance to possible damage from M.alternatus. |
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