Individual study: Effects of some organic treatments on predators (Coleoptera, Carabidae) of cabbage root fly, Delia-radicum (l) (Diptera, Anthomyiidae), and on alternative prey species
Humphreys I.C. & Mowat D.J. (1994) Effects of some organic treatments on predators (Coleoptera, Carabidae) of cabbage root fly, Delia-radicum (l) (Diptera, Anthomyiidae), and on alternative prey species. Pedobiologia, 38, 513-518
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Use organic rather than mineral fertilizers
A replicated, randomized, controlled trial in 1986-1987 in Northern Ireland (Humphreys & Mowat 1994) found ground beetle (Carabidae) abundance was higher in plots of Brussels sprouts Brassica oleracea that received mineral fertilizer followed by organic (manure or slurry) fertilizer applications compared to control plots receiving mineral fertilizers only. Over the three year period, more ground beetles were caught in no-barrier pitfall traps in the manure or slurry-treated plots than control (inorganic fertilizer-only) plots (average number of total ground beetles/trap/day: 0.46 manure plots, 0.39 slurry, 0.36 control, 0.26 straw). Ground beetles were more abundant in manure plots than controls for both barrier and no-barrier traps. In 1985 and 1986 within the planted area of plots, total catches of ground beetles were 13% and 5% higher in manure and slurry plots and 26% lower in straw plots compared with controls. The most common ground beetle, Bembidion lampros, was also more abundant in manure plots than controls. In 1985 and 1986 the largest number of springtails (Collembola) was found in manure plots, control plots had the lowest number of springtails. In 1985 and 1986 fly larvae (Diptera) and earthworms (Lumbricidae) were more abundant in manure and straw plots but the differences were not significant (no numbers given). The largest number of cabbage root fly Delia radicum eggs were found in slurry followed by control plots when ground beetles were excluded. There were five replicates of four 10 x 10 m plots. In 1985 and 1986 all plots were treated with 100 kg N, 50 kg P and 100 kg K/ha, followed by four different treatments: 0.5 t cattle manure/plot, 455 l cattle slurry/plot, three bales winter barley/plot, control (no additional treatment except herbicide). Plots were then treated with herbicide. Brussels sprouts were planted on 27 May in 1985 and 21 May 1986. In 1985 there were three pitfall traps/plot, recording from May-December. In each plot, five soil samples were taken from around unprotected plants and five soil samples from plants protected with a plastic barrier (6 cm high, 38 cm diameter; internal soil level raised to allow beetles to escape but not enter). Similar sampling was carried out in 1986, with beetles recorded weekly from 6 January to 2 December from three pitfall traps, and collected weekly April-December from 10 pitfall traps surrounded by plastic barriers (barriers used to stop egg predation). Cabbage root fly eggs were counted 10 June-21 October and pupae were collected from soil from four plants/plot on 10 January. No organic or inorganic fertilizers were applied to the plots in 1987 but cauliflower plants were planted in the plots and beetles and cabbage root fly egg-laying surveyed.