Host Preferences of the Flea Beetles Phyllotreta cruciferae and P. striolata (Coleoptera: Chrysomelidae) for Crucifer Seedlings

The preferences of two flea beetles, Phyllotreta cruciferae (Goeze) and P. striolata (F.), were investigated for nine cruciferous plants and for field peas. Preference was measured by the surface area damaged and by the number of beetles observed on the plants. Choice and no-choice tests were conducted in the laboratory using seedlings at the cotyledon and first-true-Ieaf stages. Both species fed exclusively on the crucifers, and both showed preferences among them. Only minor differences in the degree of host plant preferences were noted between the two flea beetle species. At the cotyledon stage, two Sinapis species were the least preferred and Brassica oleracea was the most preferred. Feeding preferences for older cotyledons were similar to those of younger cotyledons except that Sinapis alba L. ceased to be the least preferred. The feeding preferences for first true leaves differed from those of cotyledons for some hosts. These patterns were supported by the observed numbers of beetles on the various plants, although the two beetles showed different propensities to stay on the plants. It was concluded that both species show host preferences among species in the family Cruciferae (= Brassicaceae) and that these preferences can change with host age and leaf type. Feeding damage provides a more accurate measure of host plant preference than beetle counts, but neither is satisfactory for large-scale screening for antixenosis.