The influence of weeds and farmyard manure on the activity of Carabidae and other ground-dwelling arthropods in a sugar beet crop.
Pitfall traps were used in the Irish Republic to investigate the effects of weeds and the application of farmyard manure on arthropod activity in sugarbeet crops, with special attention to the activity of predators during the seedling stage of the crop. The most marked increases in species richness and abundance accompanied the establishment of weeds, well after sowing, on plots that were not treated with herbicides. These increases were greatest amongst detritivore and weed-specific herbivore species, although predacious staphylinids and parasitic Hymenoptera had similar responses. Carabids were the most abundant predators caught, but their numbers were not affected obviously by weeds. Farmyard manure increased the activity of species common early in the season such as Pterostichus strenuus and Bembidion lampros, and resulted in an immediate but temporary increase in general species diversity. Weed growth in the crop would not help reduce losses due to seedling pests because predator responses to weed establishment were too slow. The application of manure immediately encouraged beneficial arthropods, and seems, potentially, a useful and practical means of promoting natural control of pests during crop establishment.