Spatial dispersion and sequential sampling of Sitobion avenae (Fabricius) in wheat fields of SarPol-e Zahab, Kermanshah province

Wheat is one of the most important field crops in Kermanshah province. Although aphids are not among the key pests of wheat, their population and damage can increase in suitable conditions. Sequential sampling methods for estimating the population of aphids in wheat fields can be useful in pest management as they promote effective use of time to estimate population density. In this study, spatial dispersion and a fixed precision sequential sampling program were investigated for Sitobion avenae (Hom.: Aphididae) population in wheat fields of SarPol-e Zahab, Kermanshah province.
A systematic weekly sampling was conducted in two selected wheat fields in SarPol-e Zahab region during years 2015 and 2016. Samples were collected by X-shaped movement in the field and totally 30 plants were selected randomly in each occasion. Taylor power law and Iwao’s patchiness indices were used to assess the spatial dispersion of the aphid population. A sequential sampling plan was also developed using the fixed-precision method of Green for estimating the density of adults, nymphs, and total population.
The results showed that Taylor power law fitted better to data than Iwao’s patchiness regression. The sample size increased with increasing precision level from 0.25 to 0.1 and it also increased when the population density decreased. At precision level of 0.1, average sample number for estimating the total population of aphids was different from 150 spikes in a density of 15 aphids/spike to 200 spikes in a density of 0.1 aphids/spike. At precision level of 0.25, the required sample for population estimation ranged from 25 spikes for a density of 15 aphids/spike to 30 spikes in a density of 0.1 aphid/spike.
According to the results, sequential model at the precision level of 0.25 is recommended to sample S. avenae population, because of reducing the cost and sampling time. The results obtained from this study can be useful to population management of aphids in wheat fields of SarPol-e Zahab region.