温度对甜菜夜蛾核型多角体病毒流行的影响

Influence of incubation and inoculation temperatures on the epizootic of Spodoptera exigua nuclear polyhedrosis virus

在恒温条件下 ,研究了甜菜夜蛾 3龄初幼虫感染核型多角体病毒后的病死速率、病死时间分布与温度关系。结果表明 ,在2 9℃以下 ,随温度的升高 ,病死率增加 ,幼虫病死速率加快 ,病死持续时间缩短 ;该病毒的热抑制温度在 2 7℃左右。改进的Schoolfield模型、Stinner模型可很好地描述幼虫病死速率与温度关系。甜菜夜蛾种群饲毒后的每日病死率可用时间 -剂量 -死亡率模型较好地拟合 ,模型模拟值与实测值有较好的吻合 (Hosmer- L em oshow统计量检验不显著 ) ,方程中各项系数经 t检验达极显著水平 ;不同温度下的幼虫累计病死时间分布可用 Weibull模型、Gompertz模型及 L ogistic模型拟合 ,模型经 F检验显著 ,模型中各系数经 t检验均达到或接近显著水平。用剩余平方和 Q比较各模型的拟合程度 ,以 L ogistic模型拟合最好 ,Gompertz模型次之 ,Weibull模型拟合效果稍差。

Spodoptera exigua is one of the most important pests of vegetable plants grown in China, feeding mainly on the foliage and damaging the fruits. It was reported that the parasitoids and a nuclear polyhedrosis virus had a notable impact on the larvae of Spodoptera exigua——the virus is the most effective mortality factor. Epizootics in natural populations usually occurred and the temperature was one of the most important environmental factors affecting epizootics. In this paper, based on the systematic observation of temperature impacted on the early 3rd-instar host larvae in laboratory, the relationship between the virus epizootics and the temperature was studied, and several mathematical models were conducted. These results can be favorable to epizootology and field application of the virus. In our experiments, S. exigua nuclear polyhedrosis virus was obtained from Shanghai, China, and the isolation was proved to be specific for beet armworm (BA). The larvae of BA used in the experiments were collected in Shanghai greenhouse and isolated in our laboratory. The standard procedures were used as precaution against contaminating microorganisms during the experiments. The seven constant temperatures (18, 20, 23, 26, 29, 32, 35℃) were designed, the host larvae reared at a relative humidity of 85% and light of L∶D 12∶12. The experiments were repeated for 4 times, and 30～40 larvae of BA were treated each time.The results showed that (1) the virus-infected larvae started death mostly on 2～3d after pests inoculation, and reached peak on 4～5d when the early 3rd-instar larvae were treated with the virus concentration of 1.32×10~6 PIBs/mL and incubated at the constant temperature from 20℃ to 35℃. Between the temperature range of 20～29℃, it was found that mortality and death velocity of virus-infected host larvae increased, the disease death duration of host larvae obviously shorten, and the time at that point larval mortality and diseased prevalence started and peaked was correspondingly advanced accompanied with the increased incubation and inoculation temperature. The virus caused a mortality rate of 43.3% of the host larvae at 18℃, 90.6% at 29℃,but 56.2% at 32℃, which indicated the virus had a restricted thermal temperature. Based on the model (Y=-322.7362T+31.4028-0.5968T^2,R=0.9146, df=2, F=10.23, P=0.0267), the relationship between the infected larvae mortality and temperature. the restricted thermal temperature was estimated to be 26.3℃. (2) The model describing the relationship between the mean lethal rate V(T) of nuclear polyhedrosis virus to the S. exigua larvae and inoculation. Incubation temperature (T) was drawn as follows:V(T)=ρ(25℃)T/298*exp[ΔH~#_A/R(T/298-1/T)]1+exp[ΔH_H/R(1/T_(1/2H)-1/T)] Of which, R is 8.314J/(K·mol), and ρ(25℃),ΔН~#_A,ΔН_H are unknown parameters. The model can well fit to describe the relationship between mean lethal rate to SeNPV of its host larvae and the temperature. Otherwise, some observed data were also well simulated by Stinner model. (3) The Time-dosage-mortality model (q_(ij)=1-exp[-exp(γ_j+βlog_(10)(d_i))], of which, q_(ij) is the conditional mortality on the i day,γ_j,β is unknown parameters, d_i is the functionary intensity of temperature under the virus-infected larvae on the i day ) can well fit to simulate the daily distribution of disease death time of host larvae from 1 to 8d after inoculation at the temperature of 20～30℃. Hosmer-Lemoshow test showed that the theoretic values well fitted to the observed data, and t-test indicated that the parameters of the model reached a significant level. Based on the TDM model and under the constant temperature of 20, 23, 26, 29℃,the LT_(50) was estimated to be 5.725, 4.394, 3.746 and 3.286d, respectively. And the LT_(90) to be 4.999, 3.762d at 26, 29℃, respectively. (4) The cumulative diseased death time distribution could be described by S-type models (Gompertz, Logistic, Weibull). And,the stimulated result of Logistic model was better than those of Gompertz and Weibull models in terms of the nonlinear