The effects on terrestrial invertebrates of reducing pesticide inputs in arable crop edges: a meta-analysis.
Abstract
There is an increasing awareness of the need to evaluate critically the effectiveness of environmental conservation measures, and to ensure that agri-environment policies are based on the best available scientific evidence. A systematic review and meta-analysis investigated the impact of pesticide restriction in arable crop edges on naturally occurring terrestrial invertebrates. Twenty-three relevant experimental studies yielded 1094 pesticide contrasts. A standardized effect size (Hedges' g) could be calculated for 685 of these. Empirical data were available for 12 broad types of pesticide manipulation in crop edges. The majority of the data concerned the exclusion or selective use of herbicides. No reliable information was available on the ecological consequences for naturally occurring arthropods of excluding fungicides or insecticides separately from crop edges. Studies have focused on Carabidae, Heteroptera, Staphylinidae, Lepidoptera and grouped chick-food insects. Abundance of Heteroptera was up to 12.9 times higher where pesticide use was restricted. For other invertebrates, restricted use of pesticides generally either increased abundance or had no impact. Only two species exhibited a significant decrease in abundance. Restricting pesticide use in crop edges in most cases did not significantly affect Carabidae. This might be an artefact of the sampling method, which predominantly involved pitfall trapping. Generalization of the findings is hindered by ambiguous reporting in the primary studies. In most (20 out of 23) studies, the possibility of confounding between pesticide and fertilizer inputs could not be discounted. Synthesis and applications. Meta-analysis confirms that restriction of pesticide inputs in crop edges benefits arthropod populations at the edges of arable fields. However, an assumption in risk assessment that such benefits extend to invertebrate populations in adjacent sprayed areas is not supported. Moreover, the generality of the effects within crop edges is limited mainly to herbicides. This review highlights a lack of information on the ecological consequences of excluding insecticides and fungicides from crop edges, and identifies a need to improve the clarity of reporting in agro-ecology studies.