Effect of an organophosphorus insecticide on soil microbial and faunal communities.

¹Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, Scotland; ²Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, SY23 3EB, Wales; ³School of Biological Sciences, Royal Holloway, University of London, Egham, TW20 0EX, England; ⁴Institute of Grassland and Environmental Research, North Wyke Research Station, Okehampton, Devon, EX20 1NU, England.

Insecticides are commonly used in agriculture to control root-feeding pests such as leatherjackets (Tipula spp.) and beetle larvae. Chlorpyrifos [0,0 diethyl-0-(3,5,6-trichloro-2-pyridinyl) phosphorothioate] is one of the more common organophosphorus insecticides used to control leatherjackets in pasture systems. Microbial transformation is recognised as a critical factor affecting the fate and behaviour of insecticides in soil. Chlorpyrifos is poorly metabolised by soil microorganisms, which may result in accumulation and impacts on non-target soil microorganisms and fauna. However, few studies have assessed the impact of chlorpyrifos on the soil biota.

One aim of the UK NERC Soil Biodiversity Programme (http://mwnta.nmw.ac.uk/soilbio) is to increase our understanding of biological diversity and functioning in soil. As part of this programme the diversity of invertebrate root herbivores and their impact on plant biomass and soil microbial communities across a range of managed grasslands is being investigated. Chlorpyrifos has been applied to sub-plots in the field to control the main insect herbivore at the site (Tipula paludosa) and to assess the chemicals direct and indirect (removal of leatherjackets) impact on the soil biota. Chlorpyrifos controlled leatherjacket larvae in the field. However, its application also significantly reduced root production, tardigrade and nematode populations and altered microbial community structure and function. This obviously has important implications for utilisation of this compound in the field.