Sequential sampling plan of Metopolophium dirhodum (Hemiptera: Aphididae) in wheat fields

Sequential sampling plans of rose-grain aphid, Metopolophium dirhodum (Walker) were developed in wheat fields of Jalilabad region of Varamin, Iran. The aphid population was weekly sampled during 2000-2001. Each sample included 50 wheat stems, which were chosen randomly and the number of aphids was counted. This data was used to describe spatial distribution pattern of M. dirhodum by Taylor’s power law (TPL) and Iwao’s patchiness regression methods. The results indicated aggregated dispersion pattern of rose-grain aphid population in wheat fields, based on both methods. The TPL provided a better description of the aphid’s spatial distribution. Estimates of two mentioned models led to development of sequential sampling plans, using Green and Kuno methods at precision levels of D = 0.20 and D = 0.30 in terms of confidence interval, respectively. In both sequential sampling plans, the higher sample size obtained as population density decreased and it decreased when precision level increased from 0.30 to 0.20. The required sample size for the estimation of mean aphid density was approximately identical at 0.8 and 8 aphids per tiller in both Green’s and Kuno’s plans. Green’s plan was more efficient than Kuno’s model for both lower (≤ 0.8 per tiller) and higher (≥ 8 per tiller) aphid densities due to its small sample size required and less time needed for sampling. Kuno’s model required fewer samples at the intermediate density range (0.8-8 aphids per tiller) and is considered more effective than Green’s plan at this aphid's density range. However, Kuno’s model is not recommended when low aphid population density exists because it requires enormous samples of aphids.