| Chemosensory systems of phytophagous insects, especially the olfactory systemand the gustatory system, play crucial rule in the processes of host selection, feeding,mating and ovipasition behaviors. The two noctuid moths of Lepidoptera insectsHelicoverpa armigera (Hübner) and H. assulta (Hübner)(Lepidoptera: Noctuidae)have similar morphological characteristics and could be hybridized in laboratory. Butthe host breadth of two species are quit different, the H. armigera is an typicalpolyphagous species with about30families of hosts plants, while H. assulta is aoligophagous insect with only the few Solanaceae host plants such as tobacco andpepper. Therfore, what the mechanisms of host selection are between the two insectspecies? What roles of chemosensory system are in the process of host selection ofthe two herbivores insects? In this present study, the mechanism of gustatoryperception of host selection in H. armigera and H. assulta are investigated andcompared. Firstly, the electrophysiological responses of H. armigera and H. assultalarvae to host secondary metabolites and primary metabolites were measured andcompared. Secondly, the larval feeding preferences to different metabolites betweenthe two sibling species were investigated. Furthermore, the pathways and projectionpositions of gustatory nervous in taste sensilla to the central nervous system between the two sibling species were indentified. The main results are as follows.Comparisions of morphology of styloconic sensillua between H.armigera andH.assulta larvae.The length and width of conuli and centrum of the two types of styloconicsensillua of H.armigera and H.assulta larvae were measured using microscopes withdepth of field. The results show as follows（.1）The length of conuli both in the top ofmedial sensillum and in lateral sensillum of H. armigera larvae were significantlysmaller than that of H. assulta larvae. The width of conuli in the medial and lateralstyloconic sensillum between the two species were not significantly different.(2)Boththe length and the width of centrum in the medial sensillum of H.armigera issignificantly higher than those in the medial sensillum of H. assulta. Also, both thelength and the width of centrum in the lateral sensillum of H. armigera aresignificantly higher than those in the lateral sensillum of H. assulta. These resultsshowed that the whole volume of medial styloconic sensillum in H. armigera isbigger than that in H.assulta. Similarly, the whole volume of lateral styloconicsensillum in H. armigera is bigger than that in H.assulta.The gustatory electrophysiological and behaviour responses of H.armigera larvaeto different plant metabolite.The gustatory electrophysiological and behaviour responses of medial sensillumand lateral sensillum in H.armigera larvae to different plant metabolite weremeasured using single sensillum record technology. The feeding preference of H.armigera larvae to different plant metabolite were measured using leaf-discs choicesassay.The result are as follows.(1) The reponse of medial sensillum to gossypolshowed a direct concentration-dependent electrophysiological pattern while that totomatine showed a inverse one. Leaf-discs choices essay showed H. armigera larvaeprefer to feed on gossypol-treated leaf-discs.(2) The responses in both medialsensillum to proline and lateral sensillum to sucrose showed directconcentration-dependent patterns. Larvae prefer to feed on sucrose-treated leaf discs.These results showed that gossypol-sensitive cell, tomatine-sensitive cell andprofine-sensitive cell are in medial styloconic sensillum of H.armigera larvae with at least gossypol and tomatine don’t stimulating the same cell. We also proved theresponse of sucrose-sensitive cell in lateral sensilla to sucrose showed a directconcentration-dependent pattern. As far as feeding behaviors of H.armigera larvae tochemical compounds, both sucrose and gossypol induced a significant preference inleaf-disc choice essay.The gustatory electrophysiological and behaviour responses of larvae ofH.assulta to different plant metabolite.The gustatory electrophysiological responses of styloconic sensilla and feedingbehaviors in H. assulta larvae to different plant metabolites were measured usingsingle sensillum record technology and leaf-disc choices assay, respectively.Theresults are as follows.(1) Reponses of lateral styloconic sensillum to sucrose wasstrong and showed an obvious concentration-dependent pattern.(2) Reponses ofmedial styloconic sensillum to nicotine was compared high and also showed anobvious concentration-dependent pattern.(3) Reponses of lateral styloconic sensillumto capsicine was high and showed an obvious concentration-dependent pattern.The comparisons of gustatory electrophysiological and behaviour responses oflarvae of H.assulta and H.armigera to different plant metabolite.By comparing the electrophysiological responses between H. assulta and H.armigera larvae to sucrose, we found that the reponses of the lateral sensillum inH.armigera is significant higher than that in H.assulta. These results showed thatsucrose-sensitive cell and capsaicine-sensitive cell are in lateral styloconic sensillum,while nicotine-sensitive cell is in medial styloconic sensillum of H.assulta. We deducethat sucrose which defined as an symbolic stimulus determining the suitability of hostplant play a more important role in the process of host selection in H. armigera thanto that in H. Assulta, and The electrophysiological responses in lateral sensillum oflarvae of H.assulta was higher than that of H.armigera.Compared to larval ofH.armigera,H.assulta is more sensitive to capsaicine.Compared to larval ofH.armigera, the responses to high cocerntration of noctine of lateral and medialsensillum in H.assulta is higher than that of H.armigera, and the H.assulta is moresensitive to noctine. Electrophysiological responses of differently diet-experienced Helicoverpaarmigera (Hübner) larvae to sugarsThe diet-induced plasticity of gustatory cells of larvae was investigated using singlesensillum recording technology (SSR) by recording the gustatory electrophysiologicalresponses to five sugars and inositol in H.armigera with differently dietaryexperiences. Results showed as follows.(1) Frequencies of electrophysiologicalresponses to sucrose, D-(+)-glucose, maltose,(D-(+)-trehalose dehydrate, D-arabinoseand inositol in both styloconic sensilla of larvae with sucrose-feed experiences forcontinuous generations were obvious, but impulse frequencies of responses of themedial sensillum to (D-(+)-trehalose dehydrate and D-(+)-glucose were higher thanthose in lateral sensillum, which suggests both D-(+)-trehalose dehydrate sensitivecell and D-(+)-glucose sensitive cell were in medial sensillum.(2) Impulsefrequencies of responses to sucrose, D-(+)-glucose, maltose, D-arabinose and inositolin medial sensillum of wild population larvae captured directly from field were higherthan those of larvae with sucrose-feed experiences for ten generations. Impulsefrequency of responses produced by larvae between the two population to(D-(+)-trehalose dehydrate were significantly different, which indicated that thereaction mechanism to (D-(+)-trehalose dehydrate may be different from that tosucrose, inositol and other sugars.(3) Electrophysiological responses of larvae withsucrose-feed experience for ten generations to sucrose, D-(+)-glucose, maltose,D-arabinose and inositol were suppressed. However, the next generation of larvaewith sucrose-feed experience for ten generations were fed by diets without sucrose,resulting in the recovery of strong responses to four sugars as the wild population. Butthere was an exception that the impulse frequency of response to inositol was stillsuppressed, indicating that the mechanism of larvae responses to inositol is differentfrom that to sucrose, D-(+)-glucose, maltose and D-arabinose. In total, the resultssuggested that the electrophysiological responses ofThe pathways and projection position of peripheral styloconica sensilla in CNSin H.armigera and H.assulta larvaeThe neural pathways and projection position of peripheral gustatory neurons in sensilla styloconica of H.armigera and H.assulta larvae were investigated using biotintracer analysis. The results shows as follows.(1) The neuron axons in both medial andlateral sensilla of the two species entered the anterior and lateral suboesophagealganglion (SOG) via the maxillary nerves, where the axons branch in the anterior halfof the SOG with a little branchs entering the posterior of SOG, and the other branchof axons ascend into the ipsilateral circumoesophageal connective nerves and extendto the ipsilateral tritocerebrum;(2) the projections position of the gustatory neurons inthe medial and lateral sensillum of the two species are mainly lied in SOG andtritocerebrum. |
PDF Full Text Request