Plant hybrid zones as sinks for pests

The more susceptible hybrid cottonwood Populus trees acted as aphid pest sinks supporting most of the Pemphigus betae population. At least 85-100% of the aphid population was concentrated on <3% of the host population, with the center of a pest's distribution being the hybrid zone of its host. The concentration of aphids on such a small segment of the host population suggested that susceptible plants not only acted as sinks in ecological time, but may also have prevented aphids from adapting to the more numerous resistant hosts in evolutionary time. -from Author