The avoidance behavior is regarded as the method that provides first hand information about the behavior of an organism in the presence of contaminants in the soil. Very little data is found in literature regarding the effect of pesticides on tropical earthworms. Two pesticides, acephate and atrazine which are widely used in Indian tropical area were investigated for their avoidance behavior on standard species, E. fetida (ISO 2007) and on a tropical species, M. posthuma. The avoidance tests are rarely replicated on tropical species, M. posthuma in comparison to standard species, E. fetida or E. andrei. The standard avoidance test (ISO 2007) was taken into consideration for two different species of earthworm. Significant difference in the distribution of earthworms in the control and test soils was found depicting that soil composition plays a vital role in affecting the distribution of worms. The results also show higher sensitivity of E. fetida in comparison to M. posthuma in terms of avoidance response for both the pesticides. For risk assessment, the soil types and indigenous soil species of earthworms must be taken into consideration for evaluation of soil contamination. Avoidance tests forms the basis to study the molecular mechanisms underlying the receptor proteins responsible for the process of chemesthesis in annelids.
Keywords: Artificial soil; Avoidance; Chemosensation; Earthworms; Pesticides.
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