The effect of plant spacing on the number of aphids trapped over cocksfoot and kale crops

SUMMARY The response to plant spacing by flying and landing aphids has been studied using cylindrical and horizontal sticky traps over cocksfoot and kale crops. Some aphid species showed a significant response to spacing, being caught more frequently over wide‐than close‐spaced crops; the regressions of catches over widely‐spaced on those over close‐spaced plants suggested that most of the species caught followed this trend irrespective of the host plant. The landing response to spacing on horizontal traps at 0.3 m was normally greater than that on cylindrical traps at 1 m. At 1 m, some species (e.g. Aphis fabae gp.) gave a different response to spacing in the two crops, whilst others (e.g. Rhopalosiphum oxyacanthaé ) responded similarly to both crop spacings. In contrast to previous results with other aphid species and spaced groundnuts, the landing response of Rhopalosiphum spp. was elicited both when there was a cover crop (clover) between widely‐spaced drills of cocksfoot and by widely‐spaced cocksfoot alone. It is suggested that one stimulus eliciting the landing response with widely‐spaced plants is the electromagnetic emission from bare earth between the plants. Aphid landing behaviour was influenced by the spacing of both cocksfoot and kale plants.