Edge effect on the dynamics of pests and natural enemies in cotton agroecosystems

Investigation on the population dynamics of pests and natural enemies on the cotton plants in the middle and edge of cotton agroecosystems showed that the population of the 2nd generation of cotton bollworms ( Heliocopavar armigia ) abstract and seedling aphids ( Aphis gossyppi ) abstract was respectively 1.94 times and 1.09 times higher, but that of the 3rd generation cotton bollworms and summer aphids population was respectively 62.12% and 97.73% lower in the edge than in the middle of cotton agroecosystem. The population of predacious ladybeetles, predacious bugs, spiders and parasites in the edge of cotton agroecosystem was 73.81%, 35.79%, 52.90% and 39.11% of that in the middle of cotton agroecosystem, respectively. The greater diversity of pest community and the less diversity of natural enemies community were found in the edge than in the middle of cotton agroecosystem. The increase of energy utilization efficiency and gross production in the edge of cotton agroecosystems showed the edge effect of cotton agroecosystems.