Predation rate was assessed using ‘prey surrogates’ comprising
25 cm2 water-proof sandpaper squares pinned to the
soil surface by wooden toothpicks (Merfield et al., 2004; Frank
et al., 2007). Live aphids (dorsal side uppermost) were glued
onto the sandpaper (P150, Norton) using 3 M repositionable
glue in a grid pattern with 1 cm between aphids. The blowfly
eggs were not glued onto the surface but were placed in a
similar pattern. The sandpaper sheets were pinned at the field
boundary, the field centre and midway between the two in two
transects (5 m apart) in each field and had a 225 cm2 metal
plate supported 10 cm above to protect them from rain.
Predation rate was calculated from the removal of ‘prey’
types per 24 h period during the two study periods. At each
site, each type of ‘prey’ at both densities (minimum and
maximum) was positioned 1 m apart at the locations described
above. For each prey type for each period, overall mean
prey disappearance was calculated separately from the means
of the two prey densities.
Predation rate was assessed using ‘prey surrogates’ comprising25 cm2 water-proof sandpaper squares pinned to thesoil surface by wooden toothpicks (Merfield et al., 2004; Franket al., 2007). Live aphids (dorsal side uppermost) were gluedonto the sandpaper (P150, Norton) using 3 M repositionableglue in a grid pattern with 1 cm between aphids. The blowflyeggs were not glued onto the surface but were placed in asimilar pattern. The sandpaper sheets were pinned at the fieldboundary, the field centre and midway between the two in twotransects (5 m apart) in each field and had a 225 cm2 metalplate supported 10 cm above to protect them from rain.Predation rate was calculated from the removal of ‘prey’types per 24 h period during the two study periods. At eachsite, each type of ‘prey’ at both densities (minimum andmaximum) was positioned 1 m apart at the locations describedabove. For each prey type for each period, overall meanprey disappearance was calculated separately from the meansof the two prey densities.
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