Abstract:

【Objective】 Dasineura jujubifolia is an important pest on jujube trees. In recent years, this pest has caused serious economic losses at the jujube base facility in Yulin City, Shaanxi Province. Understanding the spatial distribution pattern and sampling technique of jujube gall midge larvae on protected jujube trees are of great practical significance for the monitoring, prediction and control of this pest. 【Method】 Facility jujube sample plots displaying serious damage by jujube gall midge larvae were selected from April to May 2020 in Liushuhui village, Jia County, Yulin City, Shaanxi Province. First, the damaged jujube trees were examined using methods such as five-point sampling, double diagonal sampling, checkerboard sampling, parallel line sampling and Z-shaped sampling. Then, the number of jujube gall midge larvae on each facility jujube tree was counted using the whole plant survey method, and the suitability, representativeness and variations among these five methods were compared using t-test. After determining the most suitable sampling method, the spatial distribution of jujube gall midge larvae on facility jujube trees was studied using seven aggregation indexes, Iwao’s m^*-m regression analysis, and Taylor power law. 【Result】 Although all five sampling methods were suitable for the investigation of jujube gall midge larvae in facility jujube trees, the parallel line sampling method was the best performing one. The spatial distribution pattern of jujube gall midge larvae on protected jujube trees was of the aggregation type. The basic component of distribution is the mutual attraction between individuals. The greater the density, the higher the aggregation of individual groups. The larvae of jujube gall midge were clustered on facility jujube trees, caused by the joint action of environmental factors and the aggregative habit of individual larvae. According to Iwao’s m^*-m regression analysis, the optimal theoretical sampling formula for jujube gall midge larvae was obtained as: N = 3.841 6/D² (2.878 3/m + 0.176 5). When the control threshold of jujube gall midge larvae was set at four inds/plant, the formula of sequential sampling model was obtained as: $T_{(n)}=4 n \pm 7.4214 \sqrt{n}$. If 100 facility jujube trees are investigated, and the cumulative number of jujube gall midge larvae is greater than 474, they need to be controlled. 【Conclusion】 The parallel line sampling method was determined to be the most suitable investigation method for jujube gall midge larvae on facility jujube trees. The spatial distribution of jujube gall midge larvae on facility jujube trees is of the aggregation type, which provides a theoretical support for the prevention and control of jujube gall midge larvae in facility jujube trees.

Key words: Dasineura jujubifolia, facility, jujube tree (Ziziphus jujuba), spatial distribution pattern, sampling technique