Effect of four insecticides on the pasture ecosystem

Abstract

Fensulfothion, fenitrothion, carbofuran, and DDT were applied as granules at 2.24 kg a.i./ha to the surface of a pasture. Arthropoda were heat-extracted from small soil cores and the effect of the insecticides on individual species was examined. Those species of Collembola cr Acari with populations which were reduced by the insecticide tended to inhabit the surface layers of the soil. DDT had little effect on the soil arthropods, and fenitrothion and fensulfothion, although having very different soil half lives, reduced populations of several species to a similar level. Seven weeks after treatment carbofuran-treated plots had higher populations of many species than the control plots. It appears that some species which may have been initially reduced by the chemical later showed an increase in numbers because of less competition from the reduced earthworm populations in these plots. It is concluded that reduced populations of some species of the small decomposers (i.e., microarthropods, nematodes, Enchytraeidae), can be compensated for by increased populations of other species of this group, and reduced populations of large decomposers (predominately lumbricid earthworms in New Zealand pastures) could have deleterious effects on the pasture.