Spatial Distribution Pattern and Sampling Technique of Conogethes punctiferalis Larvae in Maize Fields

The yellow peach moth, Conogethes punctiferalis, as an agricultural insect pest, its damage to maize ears has become more and more serious in Huang-Huai-Hai maize-producing areas of China in recent years, threatening the safe production of maize and the food safety. The spatial distribution pattern is an important ecological attribute of insect population, the objective of this study is to research the spatial distribution pattern of C. punctiferalis larvae in maize fields, clarify the spatial distribution characteristics of the pest, and to provide scientific bases for formulating field sampling program of C. punctiferalis larvae in maize fields, forecasting and effective management of the insect pest on maize.

The spatial distribution pattern of the population of C. punctiferalis larvae in maize fields was studied by traditional statistical method (aggregation indexes, Taylor's power law and Iwao's regression model) and geostatistical method. Based on the Iwao's regression model, the theoretical sampling number of C. punctiferalis larvae in fields was determined, and the maximum theoretical sampling number with different admissible errors (D=0.1, 0.2, 0.3) and the putative economic thresholds (m₀=0.5, 1, 1.5, 2 larvae per plant) was also determined by the sequential sampling.

The results of the two kinds of statistical methods showed that the spatial distribution pattern of C. punctiferalis larvae belonged to aggregation distribution. The analysis of some aggregation indexes showed that spatial distribution pattern of C. punctiferalis larvae belonged to aggregation distribution. The results of Taylor's power law showed that the spatial distribution pattern of C. punctiferalis larvae belonged to aggregation distribution, and the aggregation intensity increased with the population density. The Iwao's regression model proved that the spatial distribution pattern of C. punctiferalis larvae belonged to negative binomial distribution in aggregation distributions. The parameters of semivariogram models indicated that the optimal fitting models of C. punctiferalis larvae were the spherical, exponential and linear models. The three-dimensional and two-dimensional maps from Kriging interpolations showed that the aggregation centers of C. punctiferalis larvae were located at the edges of the fields. Based on sampling technique from the Iwao's regression model, the theoretical sampling number of C. punctiferalis larvae in maize fields was determined when the confidence probability t=2 and different mean densities m=0.5, 1, 2, 3, 4, 5, 10 and 15. The maximum theoretical sampling number was also determined by the sequential sampling. Assuming t=2, D=0.1, 0.2, 0.3, when m₀=0.5 larva per plant, the maximum theoretical sampling numbers were 3 417, 854 and 380, respectively; when m₀=1 larva per plant, the maximum theoretical sampling numbers were 1 717, 429 and 191, respectively; when m₀=1.5 larvae per plant, the maximum theoretical sampling numbers were 1 150, 287 and 128, respectively; when m₀=2 larvae per plant, the maximum theoretical sampling numbers were 867, 217 and 96, respectively.

The spatial distribution pattern of C. punctiferalis larvae belongs to the negative binomial distribution in aggregation distributions, and the aggregation centers were located at the edges of the fields. The maximum theoretical sampling number based on the sequential sampling in maize fields can be used for monitoring and management of C. punctiferalis larvae.