The dispersal and distribution of polyphagous predatory Coleoptera in cereals.
Observations were made on the phenology of the dispersal of polyphagous arthropod predators from their overwintering habitats in field boundaries into adjacent farmland in cereal fields in southern England from 1981 to 1984. Agonum dorsale, Bembidion lampros and Demetrias atricapillus dispersed from overwintering habitats into adjacent cereal crops by crawling. B. lampros was fully dispersed by early May and the other two species by late May. Tachyporus spp. were thought to disperse mainly by flight, T. hypnorum being fully dispersed by mid-May and T. chrysomelinus by late May. A small proportion of A. dorsale marked in field boundaries in April before dispersal began were later recaptured up to 200 m into adjacent crops later in the season.
Areas of a crop, immediately adjacent to field boundaries in which high numbers of predators had overwintered, were found to have significantly (P<0.01) higher numbers of predators that disperse by walking (A. dorsale, B. lampros and D. atricapillus) moving through them towards the centres of fields. By mid-summer, the mid-crop density of D. atricapillus was correlated with its overwintering density in surrounding field boundaries the previous winter, but this was not so in the other species. Mid-crop, mid-summer densities of A. dorsale were significantly (P<0.02) correlated with mean percentage weed cover in fields. The densities of the other species were not correlated with weed cover.
Analysis of data collected over a 10-yr period on a Sussex study area in late June revealed that significantly more D. atricapillus were found in fields surrounded by hedgerows than fields surrounded by fence-post and wire boundaries.