The Effect of Habitat Creation for Predatory Arthropods on Aphid Populations in Winter Wheat.

Abstract

Data are presented from research conducted to investigate the role of beetle banks in the biological control of cereal aphids.
A project designed to compare overwintering predator densities in a newly established beetle bank and two conventional hedgebanks over a five-year period, indicated that predator densities were similar to or greater than those in the surrounding hedgebanks by the second year of the beetle bank's establishment. Predators found overwintering on the beetle bank included many species that are considered to be important predators of cereal aphids. A further overwintering experiment, conducted over a four-year period, investigated five different grass species sown on beetle banks and a natural regeneration treatment, for their suitability in providing overwintering cover for polyphagous predators. Overall, the highest overwintering predator densities were recorded in grass species with tussocky growth forms and the lowest predator densities were recorded in treatments where the vegetation on the beetle bank had been allowed to naturally regenerate.
During the spring and summer, a predator exclusion experiment was conducted to explore the effect of polyphagous predators emigrating from a beetle bank on cereal aphid populations in an adjacent crop of winter wheat. The results from this experiment indicated that polyphagous predators significantly reduced aphid populations in the crop, though the impact of polyphagous predation appeared to decrease with increasing distance away from the beetle bank. The results from the exclusion experiment, together with the results from a further experiment investigating the effect of the presence or absence of a beetle bank on the distribution of polyphagous predators in crops, also indicated that beetle banks aid the rapid colonisation of cereal fields by polyphagous predators in the early spring, when the potential for aphid control is optimal.
Cost-benefit analysis suggested that an aphid population kept below spray threshold levels by enhanced natural enemy populations emigrating from a beetle bank, could result in a small but potentially useful saving in insecticide costs. The results are discussed in the context of current agricultural policies and in relation to benefits of reducing the reliance upon chemical methods to control cereal aphids. Further research needs are also identified.