Effects of weedy field margins on Myzus persicae (Hemiptera : Aphididae) in a broccoli agroecosystem

Increases in vegetational diversity have been associated with reductions in numbers of herbivorous insect pests in many agricultural settings. One man ifestation of increased vegetational diversity is the inclusion of weedy ve getation around crop plots. Plots of broccoli in a agroecosystem field stud y were surrounded by either (i) bare ground, or (ii) weedy margins, and num bers of both apterous and alate green peach aphids, Myzus persicae (Sulzer) , on broccoli were recorded. Cages designed to exclude aphid predators and parasitoids were placed on broccoli plants in both types of treatment plots . Broccoli plots surrounded by bare ground had aphid densities four times a s high as broccoli plots surrounded by weeds. Furthermore, alate aphid dens ities in plots surrounded by bare ground were five times those in weedy plo ts. This result coupled with the results of the exclusion cage experiment i ndicate that slate colonization may play an important role in the efficacy of weedy margins as a means of reducing aphid pests on broccoli.