Effects of Botanical Composition of Pastures on Insect Pest Populations

Abstract

Summary Recent studies have shown that populations of grass grub Costelytra zealandica (White), black beetle Heteronychus arator Fabricius, and white-fringed weevil Graphognafhus leucoloma (Boheman) are markedly influenced by pasture and forage crop species. Grass grub population increases are much greater under favourable legumes such as Trifolium spp. than under grasses. Populations are suppressed by unfavourable species such as Lotus pedunculatus, Medicago sativa, and Phalaris tuberosa. Populations under grass-legume mixtures are similar to those under the pure legume. In contrast to grass grub, black beetle population increases are greater under mosi grasses than under legumes, but, like grass grub, are suppressed by phalaris. White-fringed weevil populations increase rapidly in legume-dominant swards but are suppressed in pure grass pastures. These results suggest that it may be possible to prevent pest populations from increasing to severely damaging levels by manipulation of the botanical composition of pastures. This could involve both the use of unfavourable plant species and the temporary or permanent reduction or elimination of highly favourable species.