Within-plant distribution of Aulacorthum solani (Hemiptera: Aphididae), on various greenhouse plants with implications for control.

Foxglove aphid, Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae), has recently undergone a status change from an occasional pest to a serious pest in greenhouses of North America and the United Kingdom. Little nonanecdotal information exists on the ecology of this insect in greenhouse crops. To help improve integrated pest management decisions for A. solani, the within-plant distribution of this pest was explored on a variety of common greenhouse plants in both the vegetative and flowering stage. This aphid generally was found on lower leaves of vegetative plants, but was found higher in the canopy on reproductive plants (on flowers, flower buds, or upper leaves). Aphid numbers were not consistently positively correlated with total leaf surface areas within plant strata across plant species. Thus, the observed differences in preferred feeding sites on vegetative versus flowering plants are possibly a response to differences in nutritional quality of the various host-plant tissues. Despite being anecdotally described as a "stem-feeding aphid," A. solani was rarely found feeding on stems at the population densities established in our tests, with the exception of racemes of scarlet sage (Salvia splendans). Although some previous reports suggested that A. solani prefers to feed on new growth of plants, our results indicate that mature leaves are preferred over growing tips and young leaves. The implications of the within-plant feeding preferences of A. solani populations with respect to both biological and chemical control are discussed.