Individual study: Manipulation of overwintering habitats for invertebrate predators on farmland
Thomas M.B. (1991) Manipulation of overwintering habitats for invertebrate predators on farmland. PhD thesis. University of Southampton.
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Create beetle banks
A replicated, randomized study in spring 1988-1990 on one beetle bank on a mixed farm in north Hampshire, UK (Thomas 1991) found weak evidence for a shift of predatory invertebrate activity from the beetle bank into the wheat crop over time. Individuals of the ground beetle (Carabidae) Demetrias atricapillus were more abundant on or very near the beetle bank in the first half of the study period (on average 12.2 individuals/m2 at 0-3 m distance from the beetle bank 14 April-3 May 1989) after which they were more evenly distributed (on average 0.4/m2 at 0-60 m from the beetle bank 8-22 May 1989) in 1989-1990. There was no consistent pattern in the distribution of the rove beetle (Staphylinidae) Tachyporus hypnorum in 1989-1990, although lower numbers were found on the beetle bank than in the crop by the end of the study in 1989. Money spiders (Linyphiidae) were more abundant on the beetle bank than in the crop, and significantly so for all but one sample date in 1989. There was evidence of some dispersal of money spiders and limited crop invasion by wolf spiders (Lycosidae) in spring 1990. The beetle bank was created in autumn 1986 through two-directional ploughing, it was 0.4 m high, 1.5 m wide and 290 m long. The bank crossed a 7 ha field with chalky-flint soil. The crop during the study was winter wheat in all years. The beetle bank was treated with a broad-spectrum herbicide in spring 1987 to remove broad-leaved herbs before the different treatments were hand-sown. Six replicates of each treatment (four single grass species, two mixes of three or four of the grass species, and bare ground) were created. Predation pressure was studied by placing dishes of prey at different distances along transects running from the beetle bank out into the crop (in 1988: 0, 1, 5 and 15 m, in 1989: 0, 3, 10, 30 and 60 m). The number of prey items remaining after 24 h was recorded. Dishes were active over one 24-h-period/week for seven weeks. Dispersal into the crop was studied by taking weekly vacuum-net samples along five of the same cock’s-foot Dactylis glomerata transects as above in 1989 (this part of the study is also reported in (Thomas et al. 1991)). In 1990, 10 perpendicular transects of barrier pitfall traps were placed at regular intervals along the beetle bank, avoiding non-grass treatments. Traps were placed 1, 4, 20 and 50 m into the crop, and set for one three-day-period each week and then emptied weekly throughout April and May. Vacuum-net samples were also collected in 1990 from five transects adjacent to five cock’s-foot plots but at the same distances as the barrier pitfall traps. This study was part of the same experimental set-up as (Thomas et al. 1991, Thomas et al. 1992, MacLeod 1994, MacLeod et al. 2004).
Create beetle banks
A replicated, randomised study in spring 1988-1990 on a beetle bank in a 7 ha winter wheat Triticum sp. field in Hampshire, UK (Thomas 1991) found that over the 1988 survey period, predatory invertebrate activity shifted from the beetle bank into the crop, although the effect was small. In 1989, the ground beetle Demetrias atricapillus was initially more abundant 0-3 m from the beetle bank (average 12.2 individuals/m², 14 April-3 May) but became more evenly distributed with an average 0.4 individuals/m² at 0-60 m from the bank (8-22 May). The rove beetle Tachyporus hypnorum did not show a consistent distribution in 1989-1990, although fewer individuals were found on the bank than the crop by the end of the 1989 survey. More money spiders (Linyphiidae) were found in the beetle bank than the crop in 1989 and in 1990 there was a slight emigration of money spiders away from the bank into the crop. In 1990 wolf spiders (Lycosidae) were found throughout the crop but were most abundant next to the beetle bank. The beetle bank (290 m long, 0.4 m high and 1.5 m wide) was created in autumn 1986 and sown with grasses. This study was part of the same experimental set-up as Thomas et al. 1991, Thomas et al. 1992, MacLeod 1994 and MacLeod et al. 2004.