Effects of distance from field edge on aphidophagous insects in a wheat crop and observations on trap design and placement

Observations were made in a wheat crop to determine the effects on cereal aphids and their natural enemies of an adjacent crop of flowering canola (Brassica napus L.). More hoverflies (Diptera: Syrphidae) were caught adjacent to the canola than within the wheat crop, and apterous Rhopalosiphum padi (L.) (Hemiptera: Aphididae) were less numerous in the margin than at distances of64 m or more into the wheat. Large amounts of canola pollen were presentin hoverfly guts, especially for insects caught close to, or within, the canola. Earlier tests determined optimal colour, design and position of traps. Yellow traps caught most hoverflies in two six-colour comparisons of water pan traps conducted on grassed areas. In wheat, yellow water pan traps atground level caught as many hoverflies as did yellow sticky traps laid horizontally on the soil surface or vertically oriented yellow sticky traps placed at either ear height or at soil level. Only water pan traps caught large numbers of hoverfly larvae. Significantly lower numbers of Aphidius spp. (Hymenoptera: Braconidae) adults were caught on sticky traps placed at ear height within the crop than by other traps.