This study is concerned with causes of variation in the life cycles of plant.feeding insects. The aphid, Pemphigus betae , feeds on cottonwood trees during one part its life cycle and on roots of herbaceous plants at other parts. Some colonies of these insects switch between the two kinds of plants frequently while other colonies switch less often. Preliminary evidence suggests that genetic differences among aphids are partly responsible for the variation in frequency of host switching. In addition, environmental factors such as temperature and level of crowding in colonies contribute to the differences. In this study, Dr. Moran will examine how these different genetic and environmental factors interact to determine whether or not the aphids switch between hosts. Also, experiments are designed to determine whether and how life cycles of these insects are genetically adapted to local conditions of host plant availability and host plant resistance. For example, Dr. Moran will determine whether the aphids can delete the cottonwood phase of the life cycle in locations where the cottonwood trees are resistant to aphid attack. The project is also very relevant to the practical management of agricultural and forest pests. Findings will increase current understanding of how plant feeding insects evolve in response to variation in their host plants. Such evolutionary responses on the part of agricultural pests have important consequences for their economic impact on crops and forests and for the design of long.term pest control strategies.
