Comparative analysis of population characteristics of the brown planthopper,Nilaparvata lugens st?l, between wet and dry rice cropping seasons in West Java, Indonesia

Summary Population dynamics of the brown planthopper (BPH),Nilaparvata lugens St?l, were investigated in paddy fields in the coastal lowland of West Java, Indonesia, where rice is cultivated twice a year, in the wet and dry cropping seasons. Distinct differences in the basic features of population dynamics were detected between the two rice cropping seasons: (1) In the wet season, BPH populations multiplied rapidly in the period from initial to peak generation, reaching quite often the destructive level despite the low density of initial immigrants. However, in the dry season, the population growth rate and the peak population density were much lower than those in the wet season. The abundance of natural enemies such as arthropod predators played a major role in determining such a difference in seasonal population development. (2) The density at the peak generation or the occurrence of outbreaks in each field was predictable in the wet season with fairly high accuracy on the basis of the density at the initial or previous seasonal generations. In the dry season, however, the rate of population growth and the peak population density widely varied among the fields depending on the water status in each field. (3) Density-dependent processes to regulate the population density were detected in both cropping seasons. In the wet season, the regulatory processes were only detected in such high densities as cause the considerable deterioration of host plants, which suggested that the processes were largely attributable to intra-specific competition. In the dry season, however, the regulatory processes operated at a much lower density in the earlier stages of the crops. The results of an analysis of adult longevity or residence period suggested that the density-dependent dispersal of macropterous adults played an important role in stabilizing the population fluctuation among the fields in the early dry season.     

从彝族“乐比”看女性的传统教育

彝族谚语或格言(彝语称“乐比”),在彝族女性的传统教育中具有哲学意义,而且至今仍然活跃在现代彝语中.从彝语涉及女性内容的“乐比”中,能够探究出其在彝族传统社会中的重要教育作用,并折射出彝族社会女性性别的普遍意义.     

The spatial distribution pattern of the brown planthopperNilaparvata lugens St?l (Homoptera: Delphacidae) in west Java, Indonesia

Summary Spatial distribution pattern of the brown planthopper (BPH) was analyzed at 9 experimental fields in the northern part of West Java during two consecutive rice cropping seasons, i.e., wet and dry seasons. The population of each developmental stage and wing form of BPH at each location showed consistent departure from the random (Poisson) distribution, the variances of the densities in most cases exceeding their means. Namely, the distribution pattern of BPH per hill of rice plant was found to have a general tendency to be aggregated or contagious and to fit fairly well to the negative binomial model. The tendency for aggregation was further confirmed by both the β-values of -m regression being larger than unity and theC _A -values being larger than zero for each developmental stage. Although significant variations in the distribution pattern as measured by β- orC _A -value were observed between different developmental stages, between wing forms and among locations, the degree of aggregation for a given developmental stage at each experimental field remained fairly stable throughout the crop period, despite wide temporal changes in population density. Possible factors to explain these characteristics of the spatial distribution pattern of the BPH in West Java were discussed with reference to the process generating it.