Distribution pattern and optimum sample size of Wheat aphid Rhopalosiphum padi (L.) (Hemiptera: Aphididae) and their major predators

Abstract

Abstract Distribution indices such as variance to mean ratio (ID), Green's index (GI), Index of mean crowding (IMC), index of patchiness (IP), and Index of mean clumping (IDM) indicated the aggregated distribution of Rhopalosiphum padi, Coccinella. septempunctata and regular distribution of Cheilomenes sexmaculata in wheat crop. Taylor's power law regression for R.padi, C. septempunctata and C. sexmaculata showed a significant positive relationship between the mean population and variance. Aggregation parameter of Taylor's power law (b) were significantly > 1, as b = 2.039, 1.637, and 1.779, respectively in the first year, second year, and for pooled data. Iwao's mean crowding regression values were > 1 for R. padi, C.septempunctata, and C. sexmaculata with the coefficients of determination (R2) significantly high, indicating the aggregated distribution of the species. The optimum sample size (n) at 5%, 10%, and 20% precision levels for R. padi were 1265.20, 316.30, and 79.1 respectively with the mean population of R. padi as 5.0 aphids per tiller while the corresponding optimum sample size of 350 aphids/tiller, was observed to be 86.3, 21.6 and 5.4. In C. septempunctata sample size required is 324.8, 81.2, and 20.3 with a mean population of one beetle/m2 while the corresponding sample size with 18 beetles/m2 is 254.5, 63.63, and 15.9 at 5%, 10%, and 20% precision levels respectively.