Estimating an appropriate sample unit for sampling programs of alfalfa aphids in alfalfa fields

Alfalfa, Medicago sativa L. is the most widely used forage plant. In the recent decade, alfalfa aphids have become an important economic pests in some regions of Iran, including Borujerd the northern parts of Lorestan province. In this research, the appropriate sample units of alfalfa aphid populations were investigated in 2016. Comparison of six sample units, 1, 2, 3, 4, 5 and 6 of alfalfa stems revealed that there were significant difference among RV and RNP of aphid populations. Results showed that, the appropriate sample unit to estimate Acyrthosiphon pisum, Acyrthosiphon kondoi and Therioaphis maculate populations in alfalfa fields were 4, 4 and 3 stems, respectively. Based on the findings of this research, sample unit of 4 stems is recommended in the sampling for all alfalfa aphids populations in the field.