Determination of the most proper sample unit and universe of immature stages of Jasmine whitefly Aleuroclava jasmini (Takahashi) (Homo.: Aleyrodidae) on grapefruit tree

Nowadays, Jasmine whitefly Aleuroclava jasmini (Takahashi) (Homo: Aleyrodidae) is the most important pest of citrus orchards in Khuzestan province, Iran. In order to determinate the most proper sample unit and universe of Jasmine whitefly population, some experiments were carried out in a 0.8 ha grapefruit orchard using one, two or three ways factorial experimental design with three replications at different times in 2010 and 2011. Some factors like the situation of one cm2 quadrats on undersurface of leaves (five situations), four heights (0.75, 1.5, 2.5 and 3.5 m above ground level), four geographic directions and the situation of leaves on 30-40 cm branches (at 16 levels) were studied. The number of immature population was counted on the undersurface of the leaves. Using mean population (m), RV and RNP indices and regression relationships revealed that one cm2 quadrates are suitable for assessment of population. But counting the population of eggs on the mid rib at the base of the leaf and also counting the population of nymphs on the widest portion of the leaf blade were determined as the appropriate sample unit. The height of 1.5 m was considered the most suitable for sampling at all times. There was no significant difference among geographical directions for RV values, although the north direction had the highest correlation with the total population on trees, so sampling from the north direction is preferred. From the end of branch, 10th to 14th leaves on March, first to 5th leaves on April, 6th to 7th on July and 9th to 12th on January had the least values of RV, so the best leaves for sampling from branches were changed by the passage of time.