菜蚜二项式抽样设计及其精度分析

Binomial sampling models for aphids on Brassica campestris ssp. chinensis and thir sampling precision analysis

１９９０～１９９２年间对杭州市郊区青菜上桃蚜（Ｍｙｚｕｓｐｅｒｓｉｃａｅ）、萝卜蚜（Ｌｉｐａｐｈｉｓｅｒｙｓｉｍｉ）及其混合种群的田间近１００组调查数据，利用每样方（株）虫口不超过数阈值Ｔ（分别为０、１、５、１０、２０、３０、４０）头蚜虫的植株比例（ＰＴ）与种群密度（ｍ，头·株－１）的关系，通过拟合经验公式ｌｎ（ｍ）＝ａ＋ｂｌｎ［－ｌｎ（ＰＴ）］而设计的二项式抽样．通过对三者不同数阈值（Ｔ）的回归决定系数（ｒ２）、种群密度的回归估计方差（Ｖａｒ（ｍ））、抽样精度（以ｄ表示）和实际应用等的比较，结果表明当桃蚜种群处于较高密度即ｍ≥１０时，其理想的Ｔ值为３０；当萝卜蚜种群处于较高密度即ｍ≥５时，其理想的Ｔ值为１０；而它们的混合种群未得到其理想的Ｔ值．数阈值Ｔ为３０和１０可分别用于桃蚜和萝卜蚜的二项式抽样设计．而传统的二项式抽样即０～１抽样由于应用于小白菜上菜蚜的抽样设计时产生很大的误差，不宜采用．

Field sampling of aphids on Brassica campestris ssp. chinensis was conducted in the suburbs of Hangzhou from 1990 to 1992. The mean aphid density (m, number of aphids per plant), variance (s2) and the proportion of plants with no more than T defined as tally threshold (=0, 1, 5, 10, 20, 30 and 40 per plant) aphids(PT), are calculated. There are 57 estimates for Myzus persicae , 66 estimates for Lipaphis erysimi, and 38 estimates for their mixed populations. For each of two aphids and mixed population, the empirical relationship between m and PT is developed using the parameters estimated from linear regression of ln (m) on In[-ln (PT)]. The determination coefficients r2, prediction variance of m from PT, Var(m) , and sample precision denoted as d obtained from different T values are compared. The results indicate that the optimal T for M. persicae should be 30 when its m≥ 10. and that for L. erysimi should be 10 when its m≥5. However,at low population densities. no adequate T values are found for either of the two aphids. Moreover, no acceptable T is found for the mixed population. It is suggested that the tally thresholds of 30 and 10 respectively for M. persicae and L. erysimi can be used for establishing binomial sampling models under relatively high population densities. The results also show that conventional binomial sampling (0～1) method produces unacceptable low levels of sampling precision, and could not be used in sampling of the two aphids.