Cosmopolitan pests such asBrevicoryne brassicae, Lipaphis pseudobrassicae, andMyzus persicae(Aphididae) cause significant damage to Brassicaceae crops. Assessment of the important biotic and abiotic factors that regulate these pests is an essential step in the development of effective Integrated Pest Management programs for these aphids. This study evaluated the influence of leaf position, precipitation, temperature, and parasitism on populations ofL. pseudobrassicae, M. persicae, andB. brassicaein collard greens fields in the Triângulo Mineiro region (Minas Gerais state), Brazil. Similar numbers ofB. brassicaewere found on all parts of the collard green plants, whereasM. persicaeandL. pseudobrassicaewere found in greatest numbers on the middle and lower parts of the plant. While temperature and precipitation were positively related to aphid population size, their effects were not accumulative, as indicated by a negative interaction term. AlthoughDiaeretiella rapaewas the main parasitoid of these aphids, hyperparasitism was dominant; the main hyperparasitoid species recovered from plant samples wasAlloxysta fuscicornis. Parasitoids seem to have similar distributions on plants as their hosts. These results may help predict aphid outbreaks and gives clues for specific intra-plant locations when searching for and monitoring aphid populations.

Human land use threatens global biodiversity and compromises multiple ecosystem functions critical to food production. Whether crop yield-related ecosystem services can be maintained by few abundant species or rely on high richness remains unclear. Using a global database from 89 crop systems, we partition the relative importance of abundance and species richness for pollination, biological pest control and final yields in the context of on-going land-use change. Pollinator and enemy richness directly supported ecosystem services independent of abundance. Up to 50% of the negative effects of landscape simplification on ecosystem services was due to richness losses of service-providing organisms, with negative consequences for crop yields. Maintaining the biodiversity of ecosystem service providers is therefore vital to sustain the flow of key agroecosystem benefits to society.