Sampling Schemes for Estimating Populations of the Apple Aphid, Aphis pomi (Homoptera: Aphididae), on Apple 1

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Abstract
Various sampling schemes were evaluated for estimating the population size of the apple aphid, Aphis pomi DeGeer, on an apple tree. More aphids were found to inhabit the actively growing shoots in the top of the tree canopy than the bottom. An average of 90% of the total aphid population occurred on the first six leaves at the top of the tree, whereas the first four leaves contained 90% of the aphids at the bottom for all sampling dates. The method of counting the number of aphids on the most infested leaf provided the most accurate assessment of aphid density, but it required the most effort. Counting only the number of infested leaves per shoot resulted in a decrease in accuracy, but also a 4- to 8-fold decrease in the time required to sample. Reliable estimates of the aphid population over an entire tree can be made from sampling only those areas of the tree reachable from the ground. Sample size estimates are presented on the number of shoots and trees to sample, as well as an estimate of precision.

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