Impact of glyphosate on soil-dwelling and other beneficial insects
Many laboratory tests have also evaluated the toxicity of glyphosate and glyphosate-based formulations to beneficial arthropods such as spiders, beetles and mites. In a study testing the impact of glyphosate on 18 insect species, glyphosate was rated harmless for most species, slightly harmful to four species and moderately harmful to one species of carabid beetle 8.
However, the exposure conditions in the laboratory tests were highly artificial in that herbicides were applied at the maximum use rate onto artificial substrates such as glass or synthetic soil. In these conditions the organisms were forced to remain in contact with the pesticide film for several days.
In contrast, more realistic environmental exposure conditions in semi-field tests showed no effects on carabid beetles. Even when beetles were directly over-sprayed at the maximum use rate, no mortality was observed 9. The reason for the discrepancy between the laboratory and semi-field study results is very likely related to the highly artificial nature of the laboratory glass plate assays. As described above, effects observed in lower-level highly artificial studies are greatly reduced or eliminated when real exposure conditions and substrates are included.
Populations of indigenous carabid beetles and other beneficial insects have also been studied following field applications in agriculture 1, 2, 3, 11. Although shifts in population densities were observed in the weeks following treatment, plots of the data showed that these changes were associated with changes in the vegetation caused by the herbicide treatment rather than being a direct result of glyphosate toxicity 3. Other researchers have attributed the changes in carabid beetle and spider populations to the disappearance of an important food source when weeds were removed using glyphosate 1.
Additional field studies in the sandy soil of an Argentine semi-arid region have investigated the effects of glyphosate formulations on beneficial soil-dwelling insects over a period of nine months. No glyphosate-related effects were observed during this period on organisms living in the topsoil, such as mites, springtails and nematodes. Despite testing concentrations far higher than environmental exposure levels, these new studies found no impacts on springtails or predatory soil mites 7, 10.
Direct impacts on beneficial insect populations within treated field are unlikely because prolonged exposure to glyphosate based formulations is not expected. The reasons for this are because residues on plant tissue will decline quickly, transient dips in beneficial insect abundance would likely be compensated by recolonisation from areas adjacent to the treated field and rapid reproduction of the populations as vegetation re-establishes. Therefore, biologically relevant adverse effects to beneficial insect populations are not expected to occur from applications of glyphosate-based formulations.
Last update: 25 October 2012