| Despite the extensive reports on the relationships between host plants and pests as well as between pests and entomopathogens among host plant- insect pest-Beauveria bassiana interactions, the exploration into the relationship between host plants and B. bassiana is scarcely reported. Beet armyworm, Spodoptera exigua(Hübner), is one of the most serious pests damaging agricultural crops and economic crops and garden plants. B. bassiana is the most important biocontrol agents. This paper took ―plant- S. exigua –B. bassiana‖ as the object, so as to study the interaction from the aspects of ecology and physiology. The main results are as follows:1. To investigate the control effect of B. bassiana on S. exigua, this paper tested the lethal effect of four strains of B. bassiana from three different geological locations on 2nd-instar larvae of S. exigua, and fitted the lethal effect with the Time-Dose-Mortality(TDM) model. The results indicated that the median lethal concentration(LC50) for the strain BD-038(Baoding city, Hebei province), strain 2096N(Shanghai), strain A(Guangzhou city, Guangdong province) and strain B(Guangzhou city, Guangdong province) were 5.46×105~3.41×107, 1.32×107~2.31×108, 1.76×107~5.47×108, 2.94×108~6.63×109conidia·m L-1, respectively. Meanwhile, the lethal time(LT50)for strain BD-038 were 6.4854~3.6689 d at the concentrations of 1.01×106~1.01×108 conidia·m L-1, and the LT50 s for strains 2096 N and A were 4.7565 d and 5.2085 d respectively at the concentration of 1.01×108conidia·m L-1. This study revealed that the strain BD-038 had the highest toxicity to S. exigua in Shanghai.2. five-species plant-mediated effect on the susceptibility of larval S. exigua to B. bassiana was conducted. The cumulative mortalities of larval S. exigua in Ipomoea aquatica Forsk, Amaranthus tricolor, Brassica chinensis L., Glycine max and Capsicum annuum L. were 70%, 56.67%, 81.11%, 88.89% and 85.56% respectively on day 8 after treatment. This study concluded that the virulence of B. bassiana was greatest in G. max and lowest in A. tricolor.3. After the larvae were infested with B. bassiana(1.01×105conidia·m L-1) which were inoculated in the plant foliage, the durations of the 3rd-instar larvae were 1.98±0.08 d, 1.98±0.08 d, 2.07±0.09 d, 2.12±0.07 d and 2.10±0.07 d respectively in I. aquatica, A. tricolor, B. chinensis, G. max and C. annuum(with an extension of 0.07 d, 0.10 d, 0.03 d, 0.07 d and 0.02 d compared with the control groups). The durations of the 4th-instar larvae were 3.93±0.14 d, 3.73±0.15 d, 4.02±0.12 d, 4.42±0.13 d and 4.27±0.13 d IVrespectively in above five plant foliages(with an extension of 1.42 d, 1.25 d, 1.48 d, 1.87 d and 1.65 d compared with the control groups). The pupation rate of larvae were 50.0±2.2, 55.6±1.7, 47.8±1.3, 35.6±0.7 and 43.3±2.2% respectively in above five plant foliages(reduced by 34.8, 29.0, 42.4, 53.4 and 46.9% compared with the control groups). The eclosion rates were 34.3±2.5, 40.0±1.1, 34.4±1.8, 24.4±0.7 and 29.9±2.4% respectively in above five plant foliages(reduced by 45.8, 35.6, 46.8, 51.1 and 44.7% compared with the control groups). Pupal weights were 76.3±0.3, 78.7±0.3, 75.6±0.3, 76.2±0.4 and 75.1±0.6 mg in above five plant foliages(reduced by 11.1, 4.5, 8.7, 7.4 and 7.0 mg compared with the control groups). This study revealed that G. max had the strongest extension of the duration of larval S. exigua infested with B. bassiana while A. tricolor had the weakest effect.4. The lysozyme activities of larval S. exigua infested with B. bassiana began to be higher than those without B. bassiana in I. aquatica, A. tricolor, B. chinensis, G. max and C. annuum respectively from day 1 after treatments, reached the maxima on day 3 after treatments(130.4±3.2, 138.3±2.7, 126.1±1.0, 108.2±1.0 and 121.9±1.6 U/mg respectively), and began to sharply decline and constantly lower than those in the controls from day 4 after treatments. The phenoloxidase activities of larval S. exigua in the treatments began to be higher than those in the controls in I. aquatica, A. tricolor, B. chinensis, G. max and C. annuum respectively from day 1 after treatments, reached the maxima on day 2 after treatments(10.2±0.4, 9.9±0.4, 8.4±0.3, 7.9±0.8 and 8.7±0.3 U/mg respectively), and began to sharply decline and constantly lower than those in the controls from day 3 after treatments. This study expounded that host plants affected the humoral immunity of larval S. exigua infested with B. bassiana, and that the lysozyme and phenoloxidase activities in the hemolymph of host larvae were enhanced at the early stage but inhibited at the late stage when the host larvae were infested with B. bassiana.5. The protein concentration in host hemolymph and the lipid content in larval S. exigua infested with B. bassiana began to be lower than those without B. bassiana in I. aquatica, A. tricolor, B. chinensis, G. max and C. annuum respectively from day 1 after treatments, being 11.1±0.2, 11.5±0.3, 11.5±0.7, 11.3±0.7 and 12.0±0.3 mg/m L respectively for the protein concentrations and 87.6±0.2, 86.3±0.3, 87.3±0.6, 87.1±0.6 and 90.3±1.1% respectively for the lipid content. This study revealed that the lipid content in larval S. exigua infested with B. bassiana was highest in C. annuum while lowest in A. tricolor, and that the protein concentration in the hemolymph of treated host larvae was highest in C. annuum while lowest in I. aquatic. |
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