Migratory behaviour in insects correlates with reproductive development in females, and migration often occurs during the pre‐reproductive stage of adults. The relationship between ovarian development and population status of the white‐backed planthopper Sogatella furcifera (Horváth) and the brown planthopper Nilaparvata lugens (Stål) was evaluated. Females of both species were captured in rice fields and light traps and then dissected in double‐season rice‐farming regions of southern China. The ovarian development of S. furcifera and N. lugens was divided into five levels, following previous studies. The population statuses of both species were examined based on the ovarian development of female adults caught in rice paddies. The ovarian development in N. lugens females caught in light traps mostly ranged from level I to level II, whereas that in S. furcifera females caught in light traps mostly ranged from level I to level III. During peak immigration, ovarian development in N. lugens females was mainly at level II, whereas that in S. furcifera females was mainly at level II and sporadically at level III. During peak emigration, both S. furcifera and N. lugens showed level I ovarian development. The temporal dynamics of ovarian development in light trap catches revealed that (i) significant emigration and partial immigration periods occur in S. furcifera, with ovarian development mainly at level I and sporadically from level II to level III and (ii) numerous immigrants of N. lugens were detected during sedentary and local breeding periods. The temporal dynamics of ovarian development provides more information than does the paddy population. Thus, this study proposes another method for pest forecasting, which is more precise and efficient than conventional forecasting methods such as light trap catching and monitoring population dynamics in rice fields.
The effects of cycloxaprid (a modified neonicotinoid insecticide) and buprofezin (a thiadiazine insecticide) on mortality of the white-backed planthopper (WBPH), Sogatella furcifera, were determined in laboratory assays. Cycloxaprid killed WBPH nymphs and adults but buprofezin killed only nymphs, and cycloxaprid acted faster than buprofezin. One day after infestation, mortality of third-instar nymphs was >65% with cycloxaprid at 125 mg liter−1 but was <38% with buprofezin at 148 mg liter−1. By the 4th day after infestation, however, control of nymphs by the two insecticides was similar, and cycloxaprid at 125 mg liter−1 caused ≥80% mortality of adults but buprofezin at 148 mg liter−1 (the highest rate tested) caused almost no adult mortality. LC50 values for cycloxaprid were lowest with nymphs, intermediate with adult males, and highest with adult females. Although buprofezin was slower acting than cycloxaprid, its LC50 for nymphs 5 d after infestation was 3.79-fold lower than that of cycloxaprid. Mean carboxylesterase (CarE) specific activity of nymphal WBPH treated with cycloxaprid and buprofezin was higher than that of control, but there was no significant difference between cycloxaprid and control (no insecticide), and it was significantly higher for buprofezin than those of cycloxaprid and control. For glutathione S-transferase and mixed function oxygenase, the specific activity of nymphal WBPH treated with buprofezin was significantly higher than those of cycloxaprid and control, too.
Taking the data of various sectors and three industries from 1980 to 2019 as the research object, the LMDI-I (Logarithmic Mean Divisia Index) multiplicative decomposition model, which is based on the principle of decomposing the change in energy consumption into the contribution of each factor, was used to decompose the carbon emission intensity into technological progress effect and economic structure changing effect. Meanwhile, quantitative econometric models of energy price, economic growth, energy consumption structure, and the two effects were also established. The empirical results showed that energy price, economic growth, and energy consumption structure significantly influenced the reduction in carbon emission intensity. A positive U-shaped relationship between energy prices and carbon emission intensity was overserved, and the rise of energy prices mainly drive the decline of carbon emission intensity through the effect of technological progress. However, the effect of economic structure driven by the rise of energy prices was limited; thus, further optimization of economic structure is needed. Additionally, the proportion of coal consumption was positively correlated with the technological progress effect and economic structure change effect, while the decrease in coal consumption proportion promoted the decline of carbon emission intensity. Finally, three recommendations based on the analysis were proposed.
In this study, we investigated the dynamic occurrence and vertical distribution of three types of rice planthoppers (Nilaparvata lugens, Sogatella furcifera, and Laodelphax striatellus) in Shanghai, China. Our results showed that S. furcifera and L. striatellus infested the lower part of rice plants in the early development stage, S. furcifera and L. striatellus inhabited every part of rice in the middle development stage, and L. striatellus and N. lugens formicated in the upper part of the rice plant in the posterior development stage. The populations of rice planthoppers were larger in July and September, Where more than 600 adult and nymphal planthoppers, per a hundred hills of rice, were found in late July, and out of the 600, the majority were the nymphs of S. furcifera and L. striatellus. S. furcifera was mainly found from July to October, L. striatellus during the rice development, and N. lugens after September, during which their maximal individual number, per a hundred hills of rice, was 480, 220, less than 50, respectively. In addition, our results showed that adult rice planthoppers were mostly observed from late August to mid‐October with the highest population being found during mid to late September. The adult S. furcifera, L. striatellus, and N. lugens were mostly observed in August and September, from August to October, and past mid‐September, respectively. Moreover, the number of adult L. striatellus that were sticking to yellow sticky card was significantly higher than that of S. furcifera and N. lugens.
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