Comparative Studys On The Interaction Mechanism Of Two Sibling Helicoverpa Species To Tobacco Plant

Two sibling species Helicoverpa armigera(H(u|¨)bner) and H.assulta(Guenee) are serious crop pests in China.They have the similar morphological,biological and ecological characterstics,as well as they can even hybridize with each other.Their host plant ranges, however,are quite different.The former is a typical polyhpagous species,and its host plant range including at least more than 60 crop species such as cotton,corn,wheat,soybean, tobacco,and tomato,and 67 wild plant species from about 30 plant families including Malvaceae,Solanaceae,Gramineae,Leguminosae,etc.The latter is an oligophagous species with a narrower host plant range,and only feeds on plant species in Solanaceae,such as tobacco and hot pepper.In crops,H.assulta was rarely found in cotton and tomato field,and there was almost no H.armigera existing on hot pepper,only tobacco was the host plant on which both of them preferred and coexisted.In this paper,the behavioral,physiological, ecological adaption mechanism of H.armigera and H.assulta to their common host plant tobacco were studied comparatively,and the main results were summarized as follows:Electroantennogram(EAG) response of adult to tobacco volatiles:(1) H.armigera and H.assulta elicited similar EAG responses to the tested 20 tobacco volatiles;both of them elicited significantly more sensitive to green leaf volatiles,aliphatic and aromatic compounds, than to monoterpene,sesquiterpene,heterocyclic compounds under lower concentration; while the similar EAG responses under higher concentration were detected,but most of them were not significantly different with each other.(2) H.assulta elicited higher EAG responses to the most tested tobacco volatiles than H.armigera under lower concentration;however, there were no significant interspecfic differences of the two species under higher concentration.(3) There were no significant sexual differences of the two species to most of the tested tobacco volatiles under both lower and higher concentration,respectively.(4) The EAG responses of both species were positively dose-dependent to tobacco volatiles under the tested concentration range,and far from their maximum responses.Behavioral response of adult to tobacco volatiles:(1) The results of behavioral response suggested that the two species elicited significantly higher relative behavioral response to green leaf volatiles,aliphatic and aromatic compounds,than to monoterpenes, sesquiterpenes and heterocyclic compounds.(2) The relative behavioral response of mated H. assulta females to monoterpenes[α-pinene and(-)-linalool]and heterocyclic compounds (furfural) was much higher than that of H.armigera,while the response to sesquiterpenes (β-phellandrene and sabinene hydrate) was quite in the opposite,in addition,there were no significant interspecific differences of the two species.The expression of three odorant binding protein genes at different developmental stages and tissues in H.assulta:(1) Hass-PBP,Hass-GOBP₁,Hass-GOBP₂ genes were only expressed in adult stage,but not in the stages of egg,larva and pupa;and the expression quantity was irrelevant to the day-old of adult.(2) Hass-PBP,Hass-GOBP-1,Hass-GOBP₂ genes were only expressed in the antennae of adult,but not in the other parts of body,which including proboscises,head without antennae,thorax,abdomen,leg,wing;besides,Hass-PBP gene was only expressed in the antennae of male adult,while Hass-GOBP₁,Hass-GOBP₂ genes were expressed in the antennae both of male and female adult.Quantitative analysis of relative expression of GOBP₁ and GOBP₂ genes:there were no significant interspecfic and sexual differences of the relative expression quantity of GOBP₁ and GOBP₂ genes in the antenna of H.armigera and H.assulta adult.Feeding behaveor of larvae reared on two tobacco species:(1) 1^st instar of H. armigera and H.assulta larvae searched for food randomly,and did not showed any selectivity to plant leaves during the tested time scale;however,along with larvae growing up, they exhibited stronger selectivity to the tested tobacco species,and the percentage of appearance of H.armigera and H.assulta larvae on the leaves of Nicotiania tabacum were significantly higher than N.rustica.(2) Feeding time and area of H.assulta on N.tabacum leaves were significantly higher than H.armigera,but on N.rustica leaves,there were no significant interspecfic differences between H.armigera and H.assulta.Nutritional function of larvae reared on two tobacco species:(1) There were no significant differences in the approximate digestibility(AD) and relative growth rate(RGR) of 6^th instar H.armigera larvae reared on the two tobacco species;compared to the larvae feeding on N.tabacum,both the efficiency conversation of ingestion(ECI) and digestion (ECD) to N.rustica significantly decreased,while the relative consumption rate(RCR) increased significantly.(2) There were no significant differences in the relative consumption rate and approximate digestibility of 6^th instar H.assulta larvae reared on two tobacco species; compared to the larvae feeding on N.tabacum,the relative growth rate,efficiency conversation of ingestion and digestion of larvae on N.rustica significantly decreased.(3) There were no significant differences in the approximate digestibility between H.armigera and H.assulta,but the relative consumption rate and growth rate,as well as the efficiency conversation of ingestion and digestion of H.assulta reared on the two tobacco species were significantly higher than H.armigera.The effects of tobacco on the experimental population increase of H.armigera and H.assulta:(1) The development duration of H.armigera larvae were significantly prolonged when reared on N.rustica,while the survival rate of both 1^st and 2^nd instar larvae,as well as the fecundity of female adults reduced notably,so the net reproductive rate(R₀=30.5374) and innate capacity of increase(r_m=0.0951) decreased compared with those reared on N.tabacum. (2) When reared on N.rustica,the development duration of H.assulta larvae significantly prolonged,while the survival rate of each stage of larvae from 1^st to 3^rd instar and the fecundity of female adults reduced notablely,and the net reproductive rate(R₀=16.1086) and innate capacity of increase(r_m=0.0848) decreased.(3) The development and survivorship of H. assulta reared on two tobacco species were much better than H.armigera,but the ratio and fecundity of female in the H.assulta population were significantly decreased,leading to the growth rate of population lower than H.armigera.The effects of tobacco on the natural population increase of H.armigera and H. assulta:(1) The 2n^nd generation population of H.armigera in N.tabacum field(I=1.9922＞1) increased faster than that in N.rustica field;while the increase of the 3^rd generation population slowed down in N.tabacum field(I=1.5994＞1),and declined in yellow flower tobacco field(I=0.6435＜1).(2) The 2^nd generation population of H.assulta in N.tabacum tobacco field(I=1.9922＞1) increased,but declined in N.rustica tobacco field(I=0.6577＜1), the increase of the 3^rd generation population slowed down in both two tobacco fields,while the population decreasing rate was faster in N.rustica field(I=0.3592＜1)than in N.tabacum field(I=0.4571＜1).(3) The 2^nd and 3^rd generation of H.armigera increased faster than H. assulta in both N.tabacum and N.rustica tobacco field.(4) Biotic factors were important to control the population quantities of H.armigera and H.assulta;the early stage larvae were mainly affected by the factors of "predators","parasitoids","tobacco and others";while "pathogenic microorganism" had the control effects on the whole larval stage.Occurrence dynamics of population quantities of H.armigera and H.assuita in two tobacco fields:(1) The peak of occurrence with 2^nd and 3^rd generation of H.armigera in N. tabacum field was June 24 and August 7,respectively;while the duration of high occurrence period of 3^rd generation was 2.62 days longer than 2^nd generation.The peak of occurrence with 2^nd and 3^rd generation of H.assulta in N.tabacum field was seventeen and thirteen days later than H.armigera,respectively;the duration of high occurrence period of 2^nd generation of H.assulta was similar to H.armigera,but 3^rd generation of H.assulta was 3.78 days shorter than H.armigera.(2) The peak of occurrence with 2^nd and 3^rd generation of H. armigera in N.rustica tobacco field were much similar to the N.tabacum field,the duration of high occurrence period of 3^rd generation was 3.85 days longer than 2^nd generation;the peak of occurrence with 2^nd and 3^rd generation of H.assulta in N.tabacum field was eighteen and fifteen days later than H.armigera,respectively;the duration of high occurrence period of 2^nd generation of H.assulta was similar to H.armigera,but 3^rd generation of H.assulta was 4.69 days shorter than H.armigera.(3) H.armigera and H.assulta could through the separation of temporal niche to effectively avoid the interspecific competition in tobacco feld.In conclusion,the tested insects exhibited the similar olfactory sensitivity and behavioral response to tobacco volatiles between H.armigera and H.assulta,both of them could find tobacco plant accurately through tobacco volatiles,which constituting the behavioral foundations of H.armigera and H.assulta coexisted in tobacco;both of the two Helicoverpa species could feed on tobacco,and they could also complete their life cycles on tobacco, respectively,which constituting the physiological foundations of H.armigera and H.assulta coexisted in tobacco;both of the two Helicoverpa species could keep population increasing with continuous generations in tobacco,and they could effectively avoided interspecific competition to tobacco resources through the separation of temporal niche,which constituting the ecological foundations of H.armigera and H.assulta coexisted in tobacco.