Comparative Study On The Host Choice Mechanism Of Helicoverpa Armigera (Hübner) And H.assulta (Guenée)

Helicoverpa assulta (Guenée) and H.armigera (Hübner) are two sibiling species, possessing similar morphological, biological and ecological characterstics, and even hybridize with each other. However, their feeding habit are quite different. The former is an oligophagous species, and the latter is a polypagous one. Only the tobacco is the common host plant on which both species prefer and coexist. In this paper, the difference of host recognition mechanism of the two species were studied comparatively by using plant morphology, population ecology and molecular biology methods on the common host tobacco. The main results were summarized as follows:The difference of leaf trichomes and leaf substances between two species of tobacco: Nicotiania tabacum and N. rustica are only cultivated tobacco. Being the main host plants of tobacco budworm and cotton bollworm, the two tobacco species possessing different physicochemical properties. First,the leaf trichomes types of both species are long handle trichomes, short handle trichomes, non gland trichomes and branch trichomes. The branch trichomes are few in both botacco. The distribution density of long handle trichomes and short handle trichomes on N. tabacum leaf are significantly greater than N. rustica leaf. However, non gland trichomes on N. rustica leaf are significant majority. Second, the content of amylum in N. tabacum leaf is higher than N. rustica, and the content of reducing sugar, soluble sugar and nicotine were significantly lower than N. rustica, respectively.Natural population life tables of H. assulta and H. armigera on tobacco plants and the analysis of key factors: We build natural population life table of the 2nd generation H. assulta and H. armigera through three years in tobacco field. The results whowed that: First, the 2nd generation population of H. armigera in the two types of tobacco field increased faster than H. assulta, while the population of H. armigera have significant changes among different years. Second, the population growth trend of the 2nd generation population of H. armigera and H. assulta in N. tabacum field were faster than that in N. rustica field. Third, key factors influencing the 2nd generation population of H. armigera in N. tabacum field were"other factors"in first~third instar larva stages, and in N. rustica field, the key factors were"other factor"in first~third instar larva stages and"pathogenic microorganism"in fourth~sixth instar larva stages. As for H. assulta, in N. tabacum field, the key factors influencing population dynamic were as same as H. armigera in N. rustica field, while in N. rustica field, the key factor was as same as H. armigera in N. tabacum field.The expression analysis of HaGSTe1 at the mRNA and protein levels: The expression pattern of HaGSTe1 was conducted by using semi-quantitative RT-PCR, real-time PCR and prokaryotic expression. The HaGSTe1 transcript was clearly observed from the heads with antennae and proboscises removed, antennae, proboscises, thorax, legs, wings in both female and male moths, and abdomen of female moth. HaGSTe1 transcript was significantly more highly expressed in male antennae than in female antennae, suggesting that it may be involved with the decomposition of pheromones and other xenobiotics in the antenna. HassGSTe1 gene was constructed into expression vector pGEX-4T-2 for over expression in prokaryotic cells. The SDS-PAGE and Western blot analysis showed that induced by Isopropyl-β-D-Thiogalactoside (IPTG), the GST-HassGSTe1 fusion protein is expressed in Escherichia coli BL21, and its molecular weight was found to be about 51kD nearly equal to the predicted. The predicted molecular weight of Hass-GSTe1 and GST tab are 24.8 kD and 26 kD, so the expression of GST-HassGSTe1 fusion protein is effective.