EFFECT OF PESTICIDES ON MICROARTHROPODS IN SUGARCANE SOILS

THREE EXPERIMENTS WERE set up to determine whether two of the pesticides that are widely used in the sugarcane industry are detrimental to soil microarthropods. A particular focus was the effect of the pesticides on mesostigmatid mites, as they are nematophagous and help regulate populations of the nematode pests that cause damage to sugarcane. An experiment with liquid formulations of imidacloprid and bifenthrin was established at one site, while the effects of a controlled release formulation of imidacloprid were examined at two other sites. In the experiments where sugarcane was planted, the pesticides were applied to the planting furrow in a band 20 cm wide that was located 2?4 cm above recently-planted setts. Microarthropods were extracted from soil samples collected 9 weeks after the liquid formulations were applied and about 15 months after the experiments with a controlled-release formulation of imidacloprid were established. In all cases, the number and diversity of the microarthropods recovered from the samples was similar in pesticide-treated and untreated plots. Also, populations of mesostigmatid mites and their nematode prey were not affected by either bifenthrin or imidacloprid. These results indicate that the non-target effects of imidacloprid and bifenthrin on soil microarthropods are negligible, possibly because the pesticides are applied in a band in the centre of the row and much of the profile (vertically and horizontally) remains as an untreated reservoir that can be used by the organisms as a safe refuge.