Predation rate was calculated from the removal of ‘prey’
types per 24 h period during spring (November 2004) and
summer (January 2005) study periods. In each period, two prey
densities for each prey type were assessed. The aphid
densities used in November 2004 (1/25 cm2 and 4/25 cm2)
and January 2005 (4/25 cm2 and 10/25 cm2) were based on
previous studies in arable land (Ekbom et al., 1992; Winder,
1990; Winder et al., 1994). Two densities of blowfly eggs were
used, based on the literature on the abundance of carrot rust
fly egg populations. Published egg densities in the field are in
the range of 3–8/25 cm2 (Burn, 1982).