Population density sampling and dispersion pattern of Delphacodes kuscheli Fennah (Homoptera: Delphacidae) in oat crops

Abstract

Delphacodes kuscheli Fennah (Delphacidae) is the vector of the "Mal de Río Cuarto" virus, the causal agent of the most important corn disease in Argentina. Insect density, separated by developmental stage classes, sex and wing form, was estimated every 7-14 days during the spring, in an oat field in CÛrdoba Province, central Argentina, during the growing seasons of 1993 and 1994. Samples were taken with a gas-powered suction machine. Taylorís power law and Iwaoís patchiness regression models were used to describe variance-mean relationships. All insect categories showed aggregated distributions. Taylorís indices of aggregation ranged from 1.137 for brachypterous adults to 1.983 for total adults and nymphs; Iwao's density-contagiousness coefficients ranged from 1.181 for female adults to 1.686 for I-II nymphs. All regressions for both models yielded coefficients of determination of at least 0.94. Density-dependent minimum sample sizes for fixed-precision levels were determined using the estimated Taylorís coefficients. Fixed-precision-level stop lines for sequential sampling plans for each category identified were developed based on fitted Taylorís power law (Greenís method) and Iwaoís model (Kunoís method). Advantages and limitations of the plans are discussed.