ESTIMATING PREDATION OF THE GRAIN APHID SITOBION-AVENAE BY POLYPHAGOUS PREDATORS

1. The numbers of dead and live aphids falling to the ground in a cere al crop were estimated. The estimates showed that more live aphids fal l to the ground than dead ones. 2. The availability of live aphids to predators which forage on the ground was low because aphids quickly re turned to the crop canopy. This increased the relative availability of dead aphids. 3. Estimates of predation indicated that the staphylinid s Tachyporus spp., which climb plants, were the most effective polypha gous predators. 4. Models comparing the potential availability of live aphids to climbing predators and ground predators indicated that pred ators such as Tachyporus spp. were able to contact more live aphid pre y than were ground predators. 5. A comparison between polyphagous pred ators and aphid-specific hoverfly (Diptera: Syrphidae) larvae suggeste d that densities of syrphid larvae as low as 0.1 m-2 resulted in simil ar levels of predation to that accounted for by the polyphagous specie s measured in these field studies.