Sampling for Distribution of the Lettuce Aphid, Nasonovia ribisnigri (Homoptera:Aphididae), in Fields and within Heads

J. R. Mackenzie, R. S. Vernon


The lettuce aphid. Nasonovia ribisnigri (Mosley), is the most serious pest of crisphead lettuce in the lower Fraser Valley of British Columbia. To develop an efficient monitoring program. several fields of commercially grown head lettuce (cv. Ithaca) were inspected to determine the spatial distribution of the aphids. Infested plants were scattered in the fields but most often were near the margins. Therefore. to monitor for infestations, sampling should be confined to plants around the perimeters of commercial lettuce field s. Distribution within the heads was studied by infesting young plants and inspecting the leaves individually at harvest. Significantly more lettuce aphids were found on the wrapper leaves and just inside the lettuce heads than on the outer or the innermost leaves.

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